The prognostic significance of suPAR in various kidney diseases has recently been demonstrated. Its role in transplantation-specific outcomes is still largely unknown. Therefore, we prospectively investigated the prognostic relevance of suPAR in patients before and one year after kidney transplantation (KTx). We included 100 patients who had received a kidney transplantation between 2013 and 2015. The plasma concentration of suPAR was measured by ELISA assay. In recipients of living donations (LD), pre-transplant suPAR levels were significantly lower than those of recipients of deceased donations (DD). After KTx, suPAR levels significantly declined in LD and DD recipients, without a detectable difference between both groups any more. Higher suPAR levels in recipients one year after KTx were associated with a more severe eGFR loss in the following three years in multivariable cox-regression . suPAR-levels above 6212 pg/ml one year after KTx are associated with eGFR loss > 30%, which occurred almost twice as fast as in patients with suPAR ≤ 6212 pg/ml (p < 0.001). Hence, suPAR level at one year mark might be a risk indicator of increased eGFR loss. Notably, neutrophils can also serve as a major suPAR source in the bloodstream, at least in inflammatory conditions, when uPAR sheds from the neutrophil surface3. Both circulating and membrane-bound forms of suPAR are directly linked to cell adhesion and migration through binding integrins2. In the kidney, suPAR binds to and activates αvβ3 integrin on the podocyte membrane. Thereby, it contributes to podocyte foot process effacement and glomerular barrier function disruption, resulting in proteinuria5. Interestingly, it was found that uPAR-deficient mice are protected from lipopolysaccharide (LPS)-induced injury of the kidney filtration barrier. However, this protection can be reverted by the constitutive expression of αvβ3 integrin5.The soluble urokinase-type plasminogen activator receptor (suPAR) and its membrane-bound form uPAR are signaling proteins of the Ly6/alpha-neurotoxin family. They are secreted by immature myeloid cells, neutrophils, endothelial cells, smooth muscle cells, and podocytes, amongst others1.An experimental study by Hahm et al. identified bone marrow (BM)-derived immature myeloid cells as a significant source of suPAR in LPS-treated mice. Knockout mice with uPAR deficiency were irradiated and reconstituted by BM cells of uPAR wild-type mice. These chimeric mice that selectively express uPAR within hematopoietic cells showed elevated suPAR levels upon stimulation with LPS, both in the blood and urine, as well as proteinuria8. In patients experiencing autosomal dominant polycystic kidney disease (ADPKD), higher suPAR levels indicate unfavorable disease courses, even though this type of kidney disease is not caused by podocyte injury9. In congruence, Hayek et al. also showed that elevated plasma levels of suPAR indicate emerging chronic kidney disease (CKD) in persons with normal kidney functions at the baseline10. The association of suPAR with outcome measures has recently been shown to persist in hemodialysis patients12.The expression of uPAR in the kidney and the concentrations of suPAR in the blood are consistently elevated in patients with kidney diseases, especially with focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy14, acute respiratory distress syndrome (ARDS)15, or different types of cancer16.The elevation of suPAR is not solely associated with kidney diseases, but was also linked to inflammatory and diverse pathologic conditions such as rheumatologic diseases19. Regarding contrary results of different studies, Winnicki et al. showed that suPAR can serve as valuable biomarker for FSGS, but as a pitfall values must be interpreted in the context of population and test methods used considering test-specific cut-offs17. However, its role in kidney function or transplant specific outcomes needs further clarification. Therefore, we herein first prospectively investigated the prognostic relevance of suPAR in patients immediately before and one year after KTx and the influence of KTx on its values.It is still unclear whether suPAR has a pathophysiologic or prognostic role in kidney transplant (KTx) patients. At present, only a few KTx studies have tried to clarify its biomarker value for recurrent FSGS after KTxIn this study, we prospectively included 100 consented patients (age ≥ 18 years) in the final analysis who had received a kidney transplant at our transplant center between April 2013 and October 2015 and were able to provide both serum samples  for suPAR analysis. We originally enrolled a total of 160 patients, but had to exclude 60 patients who did not present to our outpatient clinic for 1-year follow-up, withdrew their consent, changed the transplant center, died (n = 7) or lost their graft (n = 2) in the first year after KTx. Mean follow-up time was 4.35 ± 1.02 years, median follow-up time 4.35 years (IQR 3.80–5.35 years), respectively.suPAR was measured in two different blood samples. The first sample was collected within 24 h before KTx, and the second was collected during a routine 1-year patient visit to our outpatient clinic. The initial immunosuppressive regimen consisted of basiliximab, tacrolimus (target trough 6–12 ng/mL), mycophenolate mofetil, and prednisolone. Anti-thymocyte globulin was administered to re-transplanted or highly immunized patients (PRA > 85%). AB0-incompatible patients received rituximab four weeks before KTx. Three patients with atypical hemolytic uremic syndrome (aHUS) as an underlying disease were given eculizumab in addition to basiliximab. Oral CMV-prophylaxis with valganciclovir was administered for 100 days in R + and 200 days in the D + /R−constellation.g using a refrigerated centrifuge, transferred into clean polypropylene tubes, and stored at − 80 °C until time of assay.Plasma concentrations of suPAR were measured using the Quantikine Human uPAR ELISA assay  according to the manufacturer’s instructions. The assay range is 62.5–4000 pg/ml, with a sensitivity of 33 pg/ml to suPAR. The samples above the concentration limit of the test were re-measured after tenfold dilution in Calibrator Diluent RD 6–10 reagent according to the manufacturer’s directions. Blood samples were collected after gaining informed consent at hospital admission within 24 h prior to KTx. The baseline and one-year samples were collected from each patient and immediately sent to the research core laboratory. The serum was obtained by centrifugation for 10 min at 2000 Patient characteristics were taken from the hospital’s electronic patient records. The data of all the participating patients was made anonymous prior to conducting an analysis. Moreover, written informed consent was obtained from all the participants. All experiments were performed in accordance with the current transplantation guidelines and the declarations of Istanbul and Helsinki. This study was approved by the local ethics committee, Ethik Kommission der Ärztekammer Westfalen-Lippe und der Medizinischen Fakultät der Westfälischen Wilhelms-Universität (No. 2013-364-f-S and No. 2019-109-f-S).20 and urine-protein/creatinine ratio (UPCR)) at years one to four after KTx. Other outcome parameters were patient and overall graft survival. Patient survival was defined as the time from KTx to death (due to any cause). When patients were lost to follow-up, the time from KTx to a patient's last contact was recorded. They were indicated as “alive”. Overall graft survival was defined as the time from KTx to death (from any cause), graft failure, or the last contact, whichever occurred first. Re-initiation of dialysis or re-transplantation was considered as graft failure. Recipients after LD and DD were considered separately21.The main outcome measures involved renal function  and/or a significant increase in proteinuria. The kidney biopsies were evaluated by two independent pathologists. The whole blood was analyzed for creatinine . Organ rejections were diagnosed as per the BANFF classification21.Data was analyzed using IBM SPSS Statistics 26 . Normally distributed continuous variables have been presented as mean ± standard deviation (SD), and non-normally distributed continuous variables were presented as median and 1st and 3rd quartiles . Absolute and relative frequencies have been provided for categorical variablesPairs of independent groups were compared using the Student’s t-test for normally distributed data, the Mann–Whitney U test for non-normal data, and the Fisher’s exact test or Chi-Quadrat-Test for categorical variables. To compare the paired data, we used the Wilcoxon test for continuous variables and the McNemar test for categorical variables.The cumulative probability of developing eGFR loss > 30% in our KTx cohort was calculated using the Kaplan–Meier analysis, and the curves were compared using the log-rank test. A cut-off for suPAR after one year for patients at higher risk for eGFR-loss was identified by calculating Youden-indices based on a ROC-analysis.To evaluate independent risk factors for the onset of eGFR loss > 30%, we performed multivariable Cox-regression analyses.Demographic and clinical characteristics have been presented in Table Patients’ outcome data have been presented in Table In patients who received LD, pre-transplant suPAR levels were significantly lower compared to those receiving DD  pg/ml, vs. 9117  pg/ml, p = 0.008). suPAR levels significantly declined in LD and DD recipients after KTx  pg/ml before KTx vs. 4376  pg/ml one year after KTx; Fig. 0,183 pg/In detail, the suPAR levels of recipients aligned without any detectable difference between those who had LD and DD  pg/ml vs. DD 4413  pg/ml, n = 100, p = 0.879, Fig. 2 , the difference was not statistically significant.In parallel, it was found that kidney function improved one year after KTx to a mean eGFR of 57.3 ± 20.1 ml/min/1.73 mDialysis vintage and cold ischemic time were significantly shorter in LD than DD recipients .Dialysis vintage tended to be associated with suPAR levels prior to KTx . Upon a closer analysis, it was seen that preemptive recipients who never underwent dialysis had significantly lower suPAR levels  pg/ml, n = 8) compared to patients on any mode of dialysis before transplantation  pg/ml, n = 92) (p = 0.006) . However, it was associated with the development of the eGFR between the second and fourth year after KTx. Higher suPAR levels one year after KTx could be associated with a higher eGFR-loss in the following three years . Patients with allograft loss were defined as eGFR-loss > 30%, patients who died with unimpaired allograft function were handled as negative for eGFR-loss > 30%. The Kaplan–Meier analysis and Log-rank test showed a significantly reduced time to eGFR-loss > 30% for patients with suPAR levels above 6212 pg/ml  and previous KTx , the Cox-regression analysis confirmed suPAR one year after transplantation as an independent risk factor for eGFR-loss > 30% .10. A recent study by Hayek et al. provided evidence that suPAR may be directly involved in the pathogenesis of acute kidney injury. Higher preprocedural suPAR levels were shown to be associated with subsequent acute kidney injury after different medical procedures, e.g. coronary angiography. These findings were experimentally confirmed in a mouse model for acute kidney injury. Mechanistically, Hayek et al. described a sensitization of kidney proximal tubules by suPAR to injury through modulation of cellular bioenergetics and increased oxidative stress in a cell culture model, which was not found for podocytes25. However, Wei et al. described a mechanism for suPAR leading to podocyte foot process effacement through the activation of αvβ3 integrin in podocytes5, thereby acting as a driver of kidney injury. Moreover, Hahm et al. reported that BM-derived immature myeloid cells are responsible for the elevated pathological levels of suPAR in the case of LPS-treated mice with proteinuric kidney disease and thus, they described suPAR as a key contributor to glomerular dysfunction1.suPAR levels are high in patients with chronic proteinuric and non-proteinuric kidney diseases and may predict disease courses26. Since data on suPAR and outcome after KTx apart from FSGS patients is still absent, we performed this prospective study.In summary, whether suPAR acts as an originator of kidney injury, is produced and/or released as a consequence of (kidney) injury, or both can occur concurrently has not been completely elucidated yet12. Additionally, since suPAR is excreted by the kidneys, end-stage renal disease may lead to an accumulation in the serum27. After KTx, the suPAR levels of both LD and DD recipients decreased to a comparable level at the 1-year mark ; otherwise, suPAR could be excreted by the working graft after transplantation, hence, kidneys seemed to have cleared suPAR from the circulation, at least in healthy volunteers30. However, our data confirmed the prognostical value of suPAR to predict the decline in functionality of the allograft  to some extent, and suPAR levels above a cut-off of 6212 pg/ml serve as a risk factor for a significantly accelerated decrease of eGFR. Notably, even after adjustment for several other known risk factors for accelerated loss of allograft function, suPAR levels remained significantly predictive for eGFR loss one year after KTx 33, had an additive protective effect for the podocyte actin cytoskeleton by tacrolimus-induced synaptopodin-mediated activation of RhoA and mycophenolate mofetil-mediated VAV1 inhibition of Rac132.Interestingly, there are interferences in the αvβ3 integrin pathway, which is induced by suPAR and calcineurin-mediated processes. These clacineurin-mediated processes are suppressed in KTx patients through the administration of calcineurin inhibitors (CNI) such as tacrolimus or cyclosporine. CNI exhibit antiproteinuric effects by stabilizing the actin cytoskeleton and stress fibers of podocytes through synaptopodin re-storage34.However, our study has limitations, as it is a single-center study and observational in nature. Further, for our study, we analyzed data of a relatively small cohort, which did not include data on non-renal causes for eGFR decline or proteinuria such as infections, CNI toxicity, or surgical problems. Another study limitation is that GFR was estimated using serum creatinine-based CKD-EPI formula instead of cystatin C-based calculation, which has some advantages, such as higher sensitivity and specificity, over creatinine measurementIn conclusion, on the one hand, our observations implicate that elevated suPAR is a consequence of kidney disease and chronical inflammation, as KTx drops suPAR levels significantly after resolving the state of end-stage renal disease. On the other hand, suPAR seems capable as an early marker for allograft dysfunction after KTx.


Elevated blood pressure is a major cause of cardiovascular morbidity and mortality. However, it is not known whether midlife blood pressure affects later life cardiovascular risk independent of later life blood pressure.P=0.001) after adjusting for genetically predicted MAP at age >55 years.Using genetic association estimates from the UK Biobank and CARDIoGRAMplusC4D consortium, univariable mendelian randomization was performed to investigate the total effect of genetically predicted mean arterial pressure (MAP) at age ≤55 years on coronary artery disease (CAD) risk, and multivariable mendelian randomization was performed to investigate the effect of genetically predicted MAP on CAD risk after adjusting for genetically predicted MAP at age >55 years. In both univariable and multivariable mendelian randomization analyses, there was consistent evidence of higher genetically predicted MAP at age ≤55 years increasing CAD risk. This association persisted after adjusting for genetically predicted MAP at age >55 years, when considering nonoverlapping populations for the derivation of MAP and CAD risk genetic association estimates, when investigating only incident CAD events after age >55 years, and when restricting the analysis to variants with most heterogeneity in their associations with MAP ≤55 and >55 years. For a 10–mm Hg increase in genetically predicted MAP at age ≤55 years, the odds ratio of later life CAD was 1.43 (95% CI, 1.16–1.77; These mendelian randomization findings support a cumulative lifetime effect of elevated blood pressure on increasing CAD risk. Clinical and public health efforts toward cardiovascular disease reduction should optimize blood pressure control throughout life. Elevated blood pressure is a powerful predictor of cardiovascular morbidity and mortality. In international surveys, the 874 million adults estimated to have a systolic blood pressure (SBP) >140 mm Hg in 2015 accounted for 106 deaths per 100 000 people and loss of 143 million disability‐adjusted life years.To optimize clinical and public health strategies toward minimizing the burden of cardiovascular disease, it is important to understand whether there is a specific period in life when elevated blood pressure increases risk, or rather whether it is that elevated blood pressure throughout life has a cumulative effect. Observational studies have shown that elevated blood pressure in midlife is associated with increased risk of cardiovascular disease in later life and represents an independent risk factor, even after adjusting for blood pressure in older age.The aim of the current study was to generate genetic instruments for mean arterial pressure (MAP) at age ≤55 years and MAP at age >55 years, and thus investigate within the MR paradigm whether genetically predicted MAP in midlife affects risk of coronary artery disease (CAD) in later life, independent of genetically predicted MAP in later life.Separate genome‐wide association study (GWAS) analyses for MAP in individuals aged ≤55 years and in individuals aged >55 years were performed in UK Biobank. These age categories were selected because they reflect the approximate transition toward increasing arterial stiffness,MAP was calculated using the mean SBP and diastolic blood pressure readings (1/3×mean SBP+2/3×mean diastolic blood pressure) obtained at baseline assessment in UK Biobank, after correcting for antihypertensive medication use by adding 15 mm Hg to SBP and 10 mm Hg to diastolic blood pressure for individuals who self‐reported use of any antihypertensive medication.P<5×10−8) and were in pair‐wise linkage disequilibrium (r2<0.001). For models 1 and 2 of the multivariable MR, instruments were selected as single‐nucleotide polymorphisms related at genome‐wide significance to MAP at age ≤55 years or to MAP at age >55 years in the GWAS analyses considering the whole UK Biobank cohort, after clumping to pairwise linkage disequilibrium (r2<0.001) on the basis of the lowest P value for association with either trait. All clumping was performed using the TwoSampleMR package in R.For univariable MR, instruments for MAP at age ≤55 years were selected as single‐nucleotide polymorphisms that associated with MAP in individuals aged ≤55 years at genome‐wide significance (librium r2<0.001. Genetic association estimates for CAD that were used in models 1 and 3 were obtained from the CARDIoGRAMplusC4D Consortium 1000G multiethnic GWAS (77% European ancestry) of 60 801 cases and 123 504 controls.International Classification of Diseases, Tenth Revision [ICD‐10]), hospital records (ICD‐10 and Office of Population Censuses and Surveys‐4), and primary care data (release readV2 and readV3). We used the following codes: ICD‐10 I20 to I25; and Office of Population Censuses and Surveys‐4 K40 to K46, K49, K50, and K75. ReadV2 and readV3 codes were extracted using a mapping from ICD‐10 codes provided by the UK Biobank (resource 592). We retained only incident events recorded after inclusion in the UK Biobank. Only white British participants aged >55 years were included in GWAS analyses, and exclusions were made for up to second‐degree related individuals (relatedness coefficient <0.0884). GWAS analysis was performed using logistic regression, with age, sex, principal components 1 to 20, genotyping chip, and assessment center included as covariates. The final sample size was 8788 cases and 184 201 controls.Genetic association estimates for CAD used in model 2 were obtained from UK Biobank participants with linked primary care data. These CAD diagnoses were derived from multiple sources: death records .The univariable and multivariable MR analyses demonstrated consistent evidence of an effect of genetically predicted MAP at age ≤55 years on CAD risk across all models Figure . For theP=0.001).The multivariable MR analysis, which adjusted the effect of genetically predicted MAP at age ≤55 years for genetically predicted MAP at age >55 years, produced smaller MR estimates with wider 95% CIs than the univariable MR analysis that did not make such an adjustment Figure . As withThis work applied the MR paradigm to generate evidence supporting an effect of midlife blood pressure on later life CAD risk independent of later life blood pressure. This finding reinforces the importance of adequate blood pressure control throughout life and is consistent with a cumulative temporal effect of elevated blood pressure on CAD risk. Our findings therefore have direct clinical and public health implications for optimizing management of blood pressure toward the goal of minimizing the burden of cardiovascular disease on both individuals and health systems.The findings of this work build on previous conventional epidemiological research that has supported a cumulative lifetime effect of blood pressure on a range of cardiovascular outcomes, including atherosclerosis, stroke, and heart failure.Our study has several strengths. To our knowledge, this is the first MR study to investigate the direct effect of genetically predicted blood pressure in midlife after adjusting for genetically predicted blood pressure in older age. Compared with conventional epidemiological research, such application of the MR approach may potentially be more robust to biases related to environmental confounding, reverse causation, and measurement error. For example, by using randomly allocated genetic variants as instrumental variables for studying the effect of modifying MAP, the MR approach that we use is able to overcome confounding from factors such as smoking and lipid status. Our study also incorporates an innovative design and comprehensive range of sensitivity analyses to explore the robustness of the findings to possible violations of the underlying assumptions of the applied MR approach. Consistent evidence supporting a direct effect of midlife blood pressure on CAD risk was obtained after adjusting for genetically predicted MAP at age >55 years, when considering nonoverlapping populations for the derivation of MAP and CAD risk genetic association estimates, when investigating only incident CAD events after age >55 years, and when restricting the analysis to variants with most heterogeneity in their associations with MAP ≤55 and >55 years.Our work also has several limitations. First, the MR paradigm measures the lifelong effect of genetic variants, and its estimates should therefore not be directly translated to assume the effect of clinical intervention on blood pressure in a given age group. Second, it was not possible to exclude the possibility that some of our analyses might have been influenced by weak instrument bias. This is particularly relevant for the multivariable MR analysis, as the associations of the genetic variants with MAP in those aged ≤55 and >55 years were closely related Tables  and S5. In conclusion, this study uses the MR approach to generate evidence supporting an effect of midlife blood pressure on later life CAD risk that is independent of later life blood pressure. These findings build on existing conventional epidemiological research, and by considering distinct populations and analytical methods, they add to the body of science supporting that it is a cumulative effect of higher blood pressure that increases cardiovascular disease risk. Clinical and public health inventions should therefore be directed toward optimizing blood pressure control across all age groups.Dr Gill is supported by the Wellcome Trust 4i Programme (203928/Z/16/Z) and British Heart Foundation Centre of Research Excellence (RE/18/4/34215) at Imperial College London. Dr Georgakis is funded by a scholarship from the Onassis Foundation. Dr Burgess is supported by a Sir Henry Dale Fellowship, jointly funded by the Wellcome Trust and the Royal Society (204623/Z/16/Z). This project has received funding from the European Union's Horizon 2020 Research and Innovation Programme (666881); SVDs@target ; CoSTREAM (Dr Dichgans); the DFG as part of the Munich Cluster for Systems Neurology ; the CRC 1123  and project DI 722/13‐1; the Corona Foundation (Dr Dichgans); the LMUexcellent Fond (Dr Dichgans); the e:Med Program ; and the FP7/2007‐2103 European Union Project CVgenes@target . The funding sources had no role in the design, acquisition of data, analysis, interpretation, or write up of this study.Dr Gill is employed part‐time by Novo Nordisk. The remaining authors have no disclosures to report.Data S1–S2Tables S1–S5References  and Click here for additional data file.


Patients with primary hyperoxaluria (PH) often develop kidney stones and chronic kidney disease. Noninvasive urine markers reflective of active kidney injury could be useful to gauge the effectiveness of ongoing treatments.A panel of biomarkers that reflect different nephron sites and potential mechanisms of injury , 8-isoprostane (8IP), monocyte-chemoattractant protein 1(MCP-1), liver-type fatty acid binding protein (L-FABP), heart-type fatty acid binding protein (H-FABP), and osteopontin (OPN)) were measured in 114 urine specimens from 30 PH patients over multiple visits. Generalized estimating equations were used to assess associations between biomarkers and 24 h urine excretions, calculated proximal tubular oxalate concentration (PTOx), and eGFR.2. After adjustment for age, sex, and eGFR, a higher urine MCP-1 concentration and MCP-1/creatinine ratio was positively associated with CaOx supersaturation (SS). Higher urine NGAL and NGAL/creatinine as well as OPN and OPN/creatinine were associated with higher eGFR. 8IP was negatively associated with PTOx and urinary Ox, but positively associated with CaOx SS.Mean (±SD) age at first visit was 19.5 ± 16.6 years with an estimated glomerular filtration rate (eGFR) of 68.4 ± 21.0 ml/min/1.73mIn PH patients greater urine MCP-1 and 8IP excretion might reflect ongoing collecting tubule crystallization, while greater NGAL and OPN excretion may reflect preservation of kidney mass and function. CaOx crystals, rather than oxalate ion may mediate oxidative stress in hyperoxaluric conditions. Further studies are warranted to determine whether urine MCP-1 excretion predicts long term outcome or is altered in response to treatment. AGXT gene, PH2 by deficiency of cytosolic and mitochondrial glyoxylate reductase/ hydroxypyruvate reductase, and PH3 by deficiency of mitochondrial 4-hydroxy-2-oxoglutarate aldolase [Primary hyperoxaluria (PH) is a group of autosomal recessive disorders characterized by recurrent urinary stones and nephrocalcinosis , 2. RougThe main biochemical defect in PH is overproduction of oxalate due to these enzyme deficiencies, primarily in the liver. The excess oxalate must then be excreted by the kidney . In the n = 24 were PH type 1, n = 4 were PH type 2, and n = 2 were PH type 3.This study was approved by the institutional review board at the Mayo Clinic, Rochester Minnesota (IRB 13–0053) and was performed in accordance with the declaration of Helsinki and all patients were consented to participate. Our study population consisted of a cohort of 30 PH patients enrolled in the Rare Kidney Stone Consortium (RKSC) PH registry between 2004 and 2013 who had one or more biobanked urine specimens and no prior history of end stage renal disease (ESRD) or organ transplantation; among these, AGXT gene, liver biopsy confirming deficiency of AGT, or by marked hyperoxaluria in combination with hyperglycolic aciduria in a patient with no identifiable secondary causes. PH2 was established by mutations of glyoxylate and hydroxypyruvate reductase gene (GRHPR), liver biopsy confirming deficiency of GRHPR enzyme, or hyperoxaluria in combination with hyperglyceric aciduria without identifiable secondary cause. PH3 was diagnosed by mutations of the 4-hydroxy-2-oxoglutarate aldolase gene (HOGA1) [General information and clinical manifestations were abstracted from Registry data. As described previously , PH1 was (HOGA1) .Laboratory results including serum creatinine, 24-h urine oxalate (UOx), calcium, citrate, creatinine, and CaOx supersaturation (CaOx SS) calculated by the computer program EQUIL2 , were exn = 47 non-stone forming adults in good general health without kidney disease or diabetes  who completed 24-h urine collections on a free choice diet served as the adult control group to establish an adult reference range for the urine biomarkers we studied. These samples were obtained from subjects participating in a reference value study. Although a lack of a prior history of kidney disease or kidney stones was confirmed, no other laboratory or dietary data was available for this group.A cohort of A 24 h urine sample was collected from patients at the time of an outpatient evaluation, centrifuged at 4 °C for 10 min at 2000 rpm, and the supernatant was frozen at -70 °C. For this study frozen aliquots were subjected to one prior freeze-thaw cycle. Urine monocyte chemoattractant protein 1 (MCP-1) was measured using the Quantikine Human chemokine (C-C motif) ligand 2/ monocyte chemoattractant protein-1 (CCL2/MCP1) ELISA kit  as previously described . Urine lP-values < 0.05 were considered statistically significant. All statistical analyses were performed using SAS, version 9.4 .All data are presented as the mean ± SD (range) or median  for normally and non-normally distributed continuous variables, respectively and n (%) for categorical variables. Urine biomarker measures as well as UOx, urine calcium/Cr, urine citrate/Cr, and PTOx were natural log transformed for analysis to account for the skewedness of the distributions. Given the wide age range of this cohort which encompasses both pediatrics and adults, urine oxalate was adjusted for body surface area (BSA) and calcium and citrate were normalized to urinary creatinine. Univariate logistic regression models were used to compare urine biomarker levels between PH patients and controls at their first visit. Odds ratios (OR) and 95% confidence intervals (95% CI) were reported from these models. The associations between the urine biomarkers and 24 h urine oxalate excretion (UOx), calculated CaOx SS, urine calcium/Creatinine (CR), urine citrate/Cr, and calculated PTOx obtained from PH patients at one or multiple time points after diagnosis were evaluated using generalized estimating equations (GEE), which estimate robust standard error to take into account the correlated nature of the specimens within patients . Paramet2 at first visit, and consisted of 53% males  had a mean ± SD age of 48.2 ± 12.8 years and were 53.2% male. Compared to adult controls, adult PH patients had higher levels of NGAL and lower levels of Clusterin, MCP 1, OPN and H-FABP, both before and after adjustment for urinary creatinine concentration . Unadjusted 8 IP concentrations were slightly lower in PH patients compared to controls, (P < 0.01). L-FABP concentrations were lower in the PH group compared to controls (P = 0.004), while no significant difference was found in creatinine-corrected L-FABP and 8 IP between cases and controls (P = 0.66) (Table 2).A total of 114 frozen bio banked urine specimens collected over multiple visits from 30 PH patients were available between 2004 and 2013. Among these 30 patients, 22 had more than one urine specimen available, ranging from 2 to 9 specimens per person over the course of 0.5 to 8.4 years. Patients in this cohort had a mean ± SD age of 19.5 ± 16.6 years and mean ± SD eGFR of 68.4 ± 21.0 ml/min.1.73m, this association remained even after adjustment for age, sex, and eGFR. 8 IP concentration was also positively associated with CaOx SS, while negatively associated with PTOx. The creatinine-corrected biomarkers L-FABP and H-FABP were both positively associated with PTOx; L-FABP was also negatively associated with CaOx SS while H-FABP was positively associated with urinary oxalate. As shown in Table Among the 30 PH patients, both unadjusted and creatinine-adjusted MCP 1 levels were positively associated with CaOx SS . The estimates and significance remained essentially unchanged  to calcium oxalate crystals resulted in increased expression of MCP-1 messenger RNA (mRNA) and protein . SimilarUrinary 8IP was also positively associated with urinary CaOx SS in the PH cohort. Studies suggest that this marker of oxidative stress is released by cells in response to oxalate and CaOx crystals, and is associated with superoxide and increased expression of NAPDH oxidase activity . PreviouThe urine of idiopathic calcium oxalate stone formers has increased amounts of N-acetyl-β-glucoseaminidase, α-glutathione S-transferase, malondialdehyde, and thiobarbituric acid reactive substances, suggesting a link between oxidative stress and stone disease in humans that parallels the observations in the hyperoxaluric rodent models . InteresOur data also suggest that higher levels of urine OPN and NGAL are associated with better kidney function. The underlying mechanism(s) may deserve further studies. OPN is a phosphorylated protein of wide tissue distribution that is found in association with dystrophic calcification including in the organic matrix of kidney stones. Although there is still debate regarding its effect upon crystal adhesion to tubular epithelial cells, studies have clearly demonstrated that OPN is a strong inhibitor of crystal formation and growth in vitro . In the Our study has certain limitations. The number of patient samples was limited and they were not collected on a protocolized basis; thus results may have been biased towards those with more severe disease. However, this is one of the larger cohorts of patients with the rare disorder of PH to have a comprehensive panel of kidney injury biomarkers assessed. Furthermore, we lacked detailed clinical data from the control population including recent dietary intakes. However, the subjects lacked a clinical diagnosis of kidney disease or kidney stone disease and were a similar subset of the group used to define the reference ranges in our laboratory for kidney stone analytes. Thus, we have no reason to suspect that there urine composition would different any systematic way from the reference values in our laboratory.Although the mechanisms are not entirely clear, CaOx crystallization in renal tubules has been considered as one of the critical therapeutic targets in the development of new therapeutic approach to treat PH. The association between urine level of MCP-1 and CaOx crystallization may suggest urine MCP-1 could be used as a marker to assist the evaluation for the effectiveness of treatments in PH patients. In addition, this association may suggest that MCP-1 signaling pathway might be in involved in the etiology of renal damage in PH. Further prospective studies are warranted to determine whether urine excretion of MCP-1 can predict long term outcomes.Additional file 1 : Supplemental Table 1 Association of urine markers with 24 urine oxalate excretion (Uox), CaOx supersaturation (CaOx SS), proximal tubular oxalate concentration (PTOx), urine calcium/Cr, and urine citrate/Cr, among n = 30 PH patients, after removing those with urine laboratory values obtained more than 1 week away from the corresponding urine biobank specimen. P-values in bold denote significance at the 0.05 level. Models were fit using the GEE procedure with the normal distribution, identity link and exchangeable correlation specifications, unless noted otherwise. Models were adjusted for age, sex and eGFR. @ Only the urine concentrations unadjusted for creatinine were used since these variables are also adjusted for creatinine. ‡Log transformations were taken for all urine biomarkers as well as Uox, PTOx, Calcium/Cr and Citrate/Cr. Units of measure are Clusterin: ng/ml and μg/g Cr; NGAL: ng/ml and ng/g Cr; 8 IP: pg/ml and ng/g Cr; MCP1: pg/ml and pg/g Cr; L-FABP: ng/ml and μg/g Cr; OPN: ng/ml and μg/g Cr; H-FABP: pg/ml and ng/g Cr.Additional file 2 : Supplemental Table 2. Association of urine markers with eGFR among n = 30 PH patients, after removing those with serum creatinine values obtained more than 1 week away from the corresponding urine biobank specimen. P-values in bold denote significance at the 0.05 level. Models were fit using the GEE procedure with the normal distribution, identity link and exchangeable correlation specifications, unless noted otherwise. Models were adjusted for age and sex. ‡Log transformations were taken for all urine biomarkers as well as Uox, PTOx, Calcium/Cr and Citrate/Cr Units of measure are Clusterin: ng/ml and μg/g Cr; NGAL: ng/ml and ng/g Cr; 8 IP: pg/ml and ng/g Cr; MCP1: pg/ml and pg/g Cr; L-FABP: ng/ml and μg/g Cr; OPN: ng/ml and μg/g Cr; H-FABP: pg/ml and ng/g Cr.


Hypertension is one of the most common cardiovascular co-morbidities after successful kidney transplantation. It commonly occurs in patients with other metabolic diseases, such as diabetes mellitus, hyperlipidemia, and obesity. The pathogenesis of post-transplant hypertension is complex and is a result of the interplay between immunological and non-immunological factors. Post-transplant hypertension can be divided into immediate, early, and late post-transplant periods. This classification can help clinicians determine the etiology and provide the appropriate management for these complex patients. Volume overload from intravenous fluid administration is common during the immediate post-transplant period and commonly contributes to hypertension seen early after transplantation. Immunosuppressive medications and donor kidneys are associated with post-transplant hypertension occurring at any time point after transplantation. Transplant renal artery stenosis (TRAS) and obstructive sleep apnea (OSA) are recognized but common and treatable causes of resistant hypertension post-transplantation. During late post-transplant period, chronic renal allograft dysfunction becomes an additional cause of hypertension. As these patients develop more substantial chronic kidney disease affecting their allografts, fibroblast growth factor 23 (FGF23) increases and is associated with increased cardiovascular and all-cause mortality in kidney transplant recipients. The exact relationship between increased FGF23 and post-transplant hypertension remains poorly understood. Blood pressure (BP) targets and management involve both non-pharmacologic and pharmacologic treatment and should be individualized. Until strong evidence in the kidney transplant population exists, a BP of <130/80 mmHg is a reasonable target. Similar to complete renal denervation in non-transplant patients, bilateral native nephrectomy is another treatment option for resistant post-transplant hypertension. Native renal denervation offers promising outcomes for controlling resistant hypertension with no significant procedure-related complications. This review addresses the epidemiology, pathogenesis, and specific etiologies of post-transplant hypertension including TRAS, calcineurin inhibitor effects, OSA, and failed native kidney. The cardiovascular and survival outcomes related to post-transplant hypertension and the utility of 24-h blood pressure monitoring will be briefly discussed. Antihypertensive medications and their mechanism of actions relevant to kidney transplantation will be highlighted. A summary of guidelines from different professional societies for BP targets and antihypertensive medications as well as non-pharmacological interventions, including bilateral native nephrectomy and native renal denervation, will be reviewed. Barring contraindications, kidney transplantation is the treatment of choice for advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD) . SurvivaSeveral immunological and non-immunological causes contribute to long-term renal and patient survival outcomes. Similar to non-transplant patients, cardiovascular diseases (CVD) remain the leading cause of morbidity and mortality in kidney transplant recipients . HyperteThis article will review the pathogenesis of post-transplant HTN, including transplant renal artery stenosis (TRAS) and differing management options based on the etiology of hypertension in different clinical transplant recipient scenarios. Determining when non-pharmacological interventions, including transplant renal artery angioplasty and/or stenting, bilateral native nephrectomy, and native renal denervation (RDN), are appropriate will also be discussed.Depending on the definition and methods of blood pressure (BP) measurement utilized, the prevalence of post-transplant HTN has been widely reported, and it has generally increased over time. This greater incidence of post-transplant hypertension maybe related to the introduction of cyclosporine (CsA) –8. A stuPost-kidney transplant HTN can be defined as a persistently elevated BP or normotension with use of antihypertensive medications after successful kidney transplantation. However, the main question that remains is what is a normal BP level? Different studies have defined post-transplant HTN with different cutoff levels for systolic and diastolic blood pressure (SBP and DBP) and different requirements for the use of antihypertensive medications. de novo HTN after kidney transplant (de novo) HTN unless otherwise specified.In addition to the defining normal BP levels, the presence or absence of HTN during the pre-kidney transplant period may further categorize kidney transplant recipients into four groups: persistent HTN, recovered HTN, persistent normotension, and post-transplant HTN. Persistent HTN occurs in patients with HTN both in the pre- and post-transplant periods, whereas patients with recovered HTN have HTN only during the pre- but not the post-transplant period. Persistent normotensive patients have no history of HTN preceding transplant and remain normotensive post-transplant. Post-transplant HTN requires developing ansplant . Malek-Hansplant  reportedIsolated forms of HTN both systolic and diastolic still occur after kidney transplantation. The European Society of Hypertension and the European Society of Cardiology guidelines defined isolated systolic HTN in the general population as SBP ≥140 and DBP <90 mmHg . This isAlternatively, diastolic HTN is defined as DBP of ≥90 mmHg, with a SBP <140 mmHg, and is more common in younger, sedentary individuals with a higher body mass index (BMI) .A recent large randomized controlled clinical trial of blood pressure management in non-diabetic patients (SPRINT) demonstrated cardiovascular (CV) benefits of tighter BP control  leading The change in prevalence of post-transplant HTN across different post-transplant periods may reflect the differences in pathogenesis of post-transplant HTN over time . IdentifDuring this time, post-transplant HTN is generally a result of external factors like transplant surgery, IV fluids, and high doses of steroids.IV fluid given during surgery and in the immediate post-operative period can lead to hypervolemia, particularly in patients with delayed graft function (DGF). A single-center cross-sectional study showed that the prevalence of hypervolemia measured by multifrequency bioimpedance analysis for extracellular fluid in stable kidney transplant recipients was 30%, and up to 5% had severe hypervolemia. This study showed that hypervolemia was significantly associated with elevated systolic, diastolic, and mean arterial pressures . AlthougSeveral indicators can be used to estimate volume status. These include conventional measurements such as BP, heart rate, urine output, central venous pressure, and pulmonary artery pressure as well as non-conventional measurements such as intraoperative transesophageal echocardiography and non-invasive dynamic cardiac output technology, e.g., pulse contour analysis, pulse wave transit time, thoracic electrical bioimpedance/bioreactance, and carbon dioxide rebreathing technologies , 30. AltHigh-dose steroids are commonly used immunosuppressive medications during the peri-transplant period. The incidence of steroid-induced HTN during the immediate post-transplant period is unknown. The mechanism of steroid-induced HTN is unclear, but it may result from alterations in intrinsic pressor response leading to arterial vascular resistance . Since aESRD patients commonly have uncontrolled HTN and require several medications to control their BP. During the immediate post-transplant period, it is common practice to hold some if not all of the pre-transplant BP medications in an effort to avoid early hypotension. However, this abrupt discontinuation of antihypertensive therapy can lead to rebound hypertension, an elevated BP above pretreatment levels, as a result of sympathetic overactivity. Beta-adrenergic agonists, clonidine  , and betSimilar to clonidine, rebound HTN from beta-blockers causes elevated BP and heart rate. It also leads to cardiac events including angina, myocardial infarction, or sudden cardiac death in patients with underlying coronary artery disease (CAD) –39. IncrAcute pain is associated with elevated BP via sympathetic nervous system activation, leading to increases in peripheral vascular resistance, heart rate, and stroke volume. In addition stimulation of the neuroendocrine system via hypothalamic-pituitary-adrenal axis leads to pain-induced HTN . InadequThere has not been a period after kidney transplantation that has been classically defined as the early post-transplant period. However, we found that systolic HTN (≥140 mmHg) occurred at the mean duration of 26–50 weeks after kidney transplantation , while t2, respectively (2) after kidney transplantation is significantly associated with post-transplant HTN —STE20/SPS1-related proline/alanine-rich kinase—Sodium Chloride Cotransporter (WNK-SPAK-NCC) pathway. CNI induces salt-sensitive HTN via activation of the WNK- SPAK-NCC pathway similarly to a rare genetic form of HTN, called familial hyperkalemic hypertension  . FHHt reSince steroids can cause HTN, steroid avoidance or withdrawal (SAW) maintenance immunosuppressive medication regimens can be considered. However, the effect of SAW on post-transplant HTN has yielded conflicting data. Curtis et al.  showed tSalt intake can lead to water retention and HTN, especially in salt-sensitive individuals . In addiA study in kidney transplant recipients who had undergone native nephrectomy before kidney transplantation from normotensive donors found that all recipients were normotensive post-transplant without need for antihypertensive therapy . Anotherde novo class II donor-specific antibodies  angiography can mitigate some of the risk of CIN, but, in most cases, small amounts of IV contrast are still required to attain sufficiently detailed images.Several imaging studies can be used to diagnose TRAS. CDU is often the initial imaging study used because it is non-invasive, widely available, and relatively inexpensive. However, the image quality and interpretation are dependent on ultrasonographer technique and experience. Peak systolic velocity (PSV) of the main renal artery and poststenotic intrarenal arterial resistive index (RI) are used to determine and grade the severity of TRAS . HoweverThree therapeutic options for TRAS are pharmacological therapy alone or pharmacologic therapy in addition to renal artery angioplasty with stenting or surgical revascularization .For pharmacological therapy, the pathophysiology of TRAS is similar to that of bilateral RAS in the non-transplant population. A decrease in renal blood flow to a transplant renal allograft causes increased RAAS activation resulting in salt and water retention and subsequent HTN. ACEI or ARB plus diuretics are a likely effective regimen for BP control. However, this pharmacologic therapy is limited by decreasing renal function resulting from decreases in systemic BP leading to reduced renal perfusion and intraglomerular pressure below the limitation of autoregulation. This increases efferent arteriolar resistance mediated by angiotensin II. By blocking the action of angiotensin II, autoregulation is blunted, and GFR is reduced . Volume Patients with worsening serum creatinine and/or uncontrolled HTN attributable to TRAS should undergo renal artery angioplasty with stenting. There is no randomized controlled clinical trial (RCT) comparing the efficacy of angioplasty ± stenting vs. surgical revascularization vs. pharmacological therapy alone in the kidney transplant population. Data from non-transplant patients from 4 RCT –99 did nApart from the above-discussed factors contributing to HTN in the early post-transplant period, some factors may contribute to HTN in the late post-transplant period.A causal relationship between chronic renal allograft dysfunction and HTN has not been proven but follows on from a logical examination of pathophysiology. Renal allograft injury—both acute and chronic—is associated with HTN. Common causes of renal allograft injury include acute allograft rejection—both acute antibody-mediated—and acute cellular rejection. Chronic renal allograft injury results from persistent antibody-mediated rejection, interstitial fibrosis/tubular atrophy, thrombotic microangiopathy, and recurrent glomerular disease in the renal allograft . An animAfter kidney transplantation, FGF23 levels decrease. The rate at which FGF23 levels normalize after transplantation is dependent on shorter dialysis vintage before kidney transplantation and the time to normalization of renal allograft function including mineral metabolism , 111. FG2 was 18, 11, and 14%, respectively. In this study, kidney transplant patients with OSA required a significantly higher number of antihypertensive medications and tended to have higher SBP as compared to non-OSA patients  in kidney transplant recipients varies with the severity of OSA. The prevalence of mild, moderate, and severe OSA in kidney transplant recipients participating in Sleep disorders Evaluation in Patients after kidney Transplantation (SLEPT) Study who had a mean eGFR of 52 ± 19 ml/min/1.73 mpatients .Similar to the non-transplant population, risk factors for OSA in kidney transplant recipients are male gender, obesity, use of hypnotic drugs, presence of severe comorbidity , and impaired kidney function . There iIn summary, the pathogenesis of post-transplant HTN may be categorized by the time period during which hypertension develops after kidney transplantation. Another approach to differentiate the etiologies of post-transplant HTN is by dividing the causes into immunological and non-immunological factors. Immunological factors, as discussed, mainly include renal allograft dysfunction and immunosuppressive medications; while non-immunological factors involve the donor, recipient, and surgical related factors .Pre-transplant BP is associated with renal allograft and patient survival outcomes after kidney transplantation. Very low pre-transplant SBP (<110 mmHg) and DBP (<50 mmHg) are associated with a decrease in renal allograft loss. Specifically during dialysis lower pre- and post-dialysis DBP are associated with better patient survival post-transplantation .During the post-transplant period, elevated BP is associated with poorer renal allograft and patient outcomes. However, as discussed above, various forms of renal allograft injury are also associated with post-transplant HTN. Several studies have demonstrated an association between post-transplant HTN and renal allograft failure –122. OpeThere is insufficient information about CV and mortality outcomes related to isolated diastolic HTN in kidney transplant recipients, and more studies are required to determine appropriate management targets for isolated diastolic HTN in this population.HTN is one of the most important risk factors for heart failure, particularly heart failure with preserved ejection fraction (HFpEF) . Kidney Renal insufficiency is involved in the pathogenesis of HFpEF  and causBP is one of the most common vital signs obtained in all clinical settings; however, it may frequently be unreliable due to variation of physiologic response to internal and external stimuli as well as inappropriate BP measurement techniques. Reliable BP measurement should be mandatory in clinical practice and can be standardized with the following definitions: the mean of three non-invasive BP measurements is referred to as office blood pressure (OBP); recording at least twice the daily average of two home blood pressure readings over a minimum of 4 days is referred to as home blood pressure monitoring (HBPM), and 24-h ambulatory blood pressure monitoring (24-h ABPM), which requires wearing an electronic blood pressure measurement device to record and averages multiple readings over a 24 h period . PurposeA 24-h ABPM provides the average of both day and night BP readings. Physiological decreases in nocturnal BP further classifies patients into dippers, non-dippers, and reverse dippers. Lee et al.  demonstrA 24-h ABPM can address and assist with the common misclassification of HTN diagnosed traditionally by OBP or HBPM. Compared with OBP, a 24-h ABPM led to 61% disagreement in diagnosis  .Although a 24-h ABPM can provide useful information to diagnose patterns of HTN like white coat and masked HTN, OBP and HBPM are more commonly used in clinical practice. Since transplant renal allografts are very sensitive to BP hemodynamic changes, HBPM appears to be a common utilized method of following BP after kidney transplantation. One study in patients who were 1–10 years after kidney transplantation revealed a higher correlation between a 24-h ABPM and HBPM than 24-h ABPM and OBP .Though elevations in both day and night SBP obtained from 24-h ABPM were associated with risk of declining renal allograft function, and nighttime elevation in SBP exhibited a stronger association . An elevAlthough HBPM is widely available, better correlated to 24-h ABPM, and superior to OBP when predicting hard outcomes, we used HBPM in conjunction with OBP for our kidney transplant patients to minimize misclassification of HTN diagnosis, monitor possible white coat or masked HTN, and adjust antihypertensive medications.Non-pharmacologic interventions, such as diet, exercise, and stress reduction, should always be part of treatment of HTN. Since the majority of kidney transplant recipients have pre-transplant HTN requiring antihypertensive medications (persistent HTN) and only small number of patients become normotensive without blood pressure medications (recovered HTN), pharmacological intervention remains the cornerstone of BP control in this population. Additionally, other interventions specific to certain etiologies of resistant HTN, such as transplant renal artery angioplasty ± stenting and treatment for OSA, should be implemented. Renal sympathetic denervation of the native kidneys either by bilateral native nephrectomy or catheter ablation is also treatment option for resistant HTN in this population . In thisA recent retrospective cross-sectional analysis from a single transplant center in Poland reported the trend of commonly used antihypertensive medications in their kidney transplant recipients over 14 years. They examined antihypertensive therapy data from transplant recipients first outpatient visits from 2001, 2006, 2011, and 2014 . Beta-bl2 agonist like clonidine, however, may need to be continued during peri-transplant period to avoid rebound HTN.The majority of advanced CKD and ESRD patients have HTN. Volume overload is the most common cause of uncontrolled BP in ESRD patients . In the Providers taking care of kidney transplant recipients have different opinions when selecting antihypertensive medications during peri- and post-transplant period. Their decision may mainly be driven by protocols or common practices followed at their kidney transplant centers. Specific information relevant to kidney transplantation should guide the selection of antihypertensive medications, but, as in other scenarios, it is rational to individualize BP management for certain kidney transplant recipients.Diuretics are not commonly used as the first line antihypertensive medication in kidney transplant recipients. They may cause volume depletion, electrolyte disturbances, and worsening renal allograft function. However, they are indicated and should not be avoided in certain patients in the peri-transplant period.Volume control rather than BP control is the indication for loop diuretics in kidney transplant recipients, especially during immediate and early post-transplant periods. Kidney transplant recipients generally receive peri-transplant IV fluid to keep up with an increased urine output from a new functioning renal allograft. Volume overload presenting with peripheral edema, pulmonary congestion, or HTN may occur when the establishment allograft function lags behind the volume resuscitation provided. Diuretics can be used to control both volume and BP in this common scenario.There is also evidences that loop diuretics have a vasodilator effect and can decrease edema, congestion, and oxygen requirements. Theoretically they can decrease ischemic renal injury and risk of DGF in kidney transplant recipients. However, despite their common use in clinical practice, there is no consistent data to support using loop diuretic to increase urine output and prevent DGF. In addition, there is no strong evidence showing an association between loop diuretic and improvement in initial or long-term graft function . On the Furosemide is the most commonly used loop diuretic. It has been used to predicting progression of AKI with the so-called furosemide stress test (FST) in non-transplant patients , 146. LoGiven the wide range of risks and benefits with loop diuretics, clinicians should individualize their use in transplant recipients. Additional RCTs are required to determine the efficacy and safety of loop diuretic in kidney transplant recipients.Thiazide diuretics are commonly used antihypertensives in general population. They are however uncommon in the management of kidney transplant recipients because of their metabolic side effects which include hyperglycemia, hyperuricemia, hypercalcemia, and hyponatremia , 148.Thiazides however, may theoretically control CNI-induced HTN. Since CNI-induced HTN is salt sensitive , 149 viaAlthough loop diuretics are generally favored over thiazide diuretic for volume control, they can lead to additional renal magnesium wasting. Thiazides can be considered in transplant patients who already have other reasons for and often struggle with hypomagnesemia. However, because CNI and loop diuretics act on the common mechanism to lower luminal electro-positivity decreasing paracellular magnesium reabsorption, using a loop diuretic in concert with CNI may not cause further urinary magnesium loss . A retroThiazides may be considered for kidney transplant recipients with CNI-induced salt-sensitive HTN and hypomagnesemia.Mineralocorticoid receptor antagonists (MCRA) have CV benefits , 156 and2. After 8 weeks of eplerenone 25 mg/d, nine out of 31 patients had serum potassium of >5 mmol/l, and one patient had serum potassium of >5.5 mmol/l. Mean baseline eGFR was 41 (26–59) ml/min/1.73 m2 after 8 week of eplerenone therapy and was not significantly different between patients who did and did not develop hyperkalemia . Having a baseline serum potassium >4.35 mmol/l was associated with increased serum potassium of >5 mmol/l once starting eplerenone  . Anotherlerenone .CNIs can cause vascular vasoconstriction via activation of mineralocorticoid receptor in smooth muscle leading to impaired renal allograft function. MCRAs bind mineralocorticoid receptors in principle cells of collecting ducts and are potentially reno-protective by blunting the renal vascular resistance induced by CNI therapy .Spironolactone decreases cardiac left ventricular volume and mass, but studies are required to determine its effect in kidney transplant recipients . In addiWith some evidence for antiproteinuric effect and their established safety in transplant recipients even when in combination with ACEI or ARB, MCRA may be a new option for BP control in individual with CNI-induced HTN and proteinuria.The cardioprotective effects and survival benefit of beta-blockers make them a favored medication in the general  and ESRDAlthough beta-blockers provide survival benefit in kidney transplant recipients, they can cause metabolic side effects, including proteinuria, hyperkalemia, and masking of hypoglycemic symptoms. Therefore, caution should be used when using beta blockers in kidney transplant recipients who are at risk to develop these side effects.Calcium channel blockers inhibit entry of calcium into vascular smooth muscle cells, resulting in vascular vasodilation . Since tIn addition to blood pressure control, calcium channel blockers also prevent post-transplant acute tubular injury (ATI) or DGF. One prospective trial looked at diltiazem use in patients who received deceased donor renal transplantation (DDRT). Participants were randomized to kidneys that had been given diltiazem (Euro-collin's solution (20 mg/l) at time donor nephrectomy; meanwhile, the recipients received a bolus injection of diltiazem (0.28 mg/kg) pre-operatively followed by an infusion 0.0022 mg/min/kg for 2 days before transitioning to oral diltiazem vs. a control group, which did not receive diltiazem but otherwise received the same induction immunosuppression regimen with CsA. The diltiazem group had lower incidence of ATI, higher GFR with primary function, and lower incidences of rejection at 1 month post-transplant. They however had higher CsA level compared to control group. The total CsA required was lower in the diltiazem group, as might be expected, to achieve comparable CsA levels between the two groups. The lower post-transplant ATI in the diltiazem group was postulated to be secondary to lower ischemic damage in the renal allograft and reduced CNI nephrotoxicity . A CochrAlthough calcium channel blockers provide better renal allograft function, several studies showed no difference in terms of BP control when using verapamil compared to enalapril or doxazosin . No diffThe evidence for the benefits of calcium channel blockers appears inconsistent; however, a recent systematic review and meta-analysis of 60 trials including 3,802 patients showed that, compared to placebo or no treatment, calcium channel blockers decreased graft loss  and increased GFR . Compared to ACEIs, patients treated with calcium channel blockers tend to have a higher GFR; although there is inconclusive data regarding graft loss between these two groups . Given tAdverse drug reactions and drug–drug interaction between calcium channel blockers and other commonly used medications should be taken into consideration. Calcium channel blockers can result in peripheral edema and muscle weakness especially when used in combination with steroids. Gum hyperplasia is also more common when calcium channel blockers are used with CsA . AlthougSince proteinuria is a surrogate marker for renal disease, lowering proteinuria is one strategy to slow the progression of CKD. ACEIs and ARBs are antihypertensive agents with known antiproteinuric effect. ACEIs inhibit angiotensin-converting enzyme, which converts renin to angiotensin. ARBs act on angiotensin II receptors and subsequently inhibit RAAS pathway. A systematic review and meta-analysis of 21 clinical trials, including 1,549 patients, revealed no difference in the MAP change between ACEI or ARB group and the control group. Serum potassium was also not different between the two groups. However, the ACEI or ARB group had a decrease in proteinuria, eGFR, and hematocrit when compared to the control group. There was insufficient data regarding the benefits of ACEI or ARB therapy in terms of patient or renal allograft survival . In the RAAS activation is associated with interstitial fibrosis and tubular atrophy (IF/TA), one of the most common causes of renal allograft loss , 184. ThACEIs and ARBs can lead to regression of LVH in kidney transplant recipients , 188, buAlthough ACEIs and ARBs provide antiproteinuric effect, they are generally not the drugs of choice during the immediate and early post-transplant periods. This is mainly because they are known to decrease GFR. This side effect is reversible, but it leads to a confusion early on differentiating their role from other causes of renal allograft dysfunction and may lead to unnecessary workups, including invasive investigation, e.g., transplant renal biopsy.While there is no robust evidence for CV or survival advantages with the use of ACEIs, ARBs, and MCRAs, these antihypertensive medications may be considered. They may be considered in transplant recipients, particularly those with LVH, congestive heart failure, and proteinuria.1-antagonists are rarely used as the initial or as a single antihypertensive agent in kidney transplant recipients. Although they reduce BP by decreasing peripheral vasoconstriction and theoretically should counteract with vasoconstrictive effect of CNI, there is no evidence that alpha1-antagonists provide superior antihypertensive effect or slows progression of renal allograft dysfunction when compared to other antihypertensive medications. A study with long-term follow up in 88 hypertensive kidney transplant recipients who were divided into three groups, verapamil, enalapril, and doxazosin, demonstrated that doxazosin provided the same efficacy in BP control compared with the others while maintaining an excellent safety profile. However, up to 38% of patients in the doxazosin group needed additional antihypertensive medications compared to only 8 and 13% in verapamil and enalapril groups, respectively  control group . This daAlthough native nephrectomy can improve post-transplant HTN, both pre- and post-transplant native nephrectomy can lead to surgical complications, which can cause impaired renal allograft function. Therefore, native nephrectomy for the purpose of BP control in kidney transplant recipients should be performed in select patients with severely uncontrolled post-transplant HTN whom, without treatment, would have deterioration of renal allograft function or be at increased risk of CV complications. Patients who undergo bilateral native nephrectomy for alternative indications such as recurrent infection, discomfort from large polycystic kidneys, or suspicious native renal tumors may have the added benefit of improved BP control.−1 kg−1) and lower body negative pressure (−27 mmHg) in 25 kidney transplant recipients and 10 normal subjects concluded that the reinnervated efferent renal nerves in the human transplanted kidney are still essentially functionally denervated (Partial reinnervation of the human transplanted kidney has been shown histologically. Axonal regeneration in a human transplant kidney started at 28 days to 5 months post-kidney transplantation and was complete within 8–12 months to 2 years , 225. Thnervated . Since cTwo reported kidney transplant recipients with resistant HTN had improved BP control after RDN of native kidneys , 230. AnHTN is a very common disease in CKD and ESRD and remains so after kidney transplantation. The pathogenesis of post-transplant HTN is complex. BP measurement is still the main barrier to accurately diagnose and follow-up in HTN management. A 24-h ABPM, though the gold standard, is inconvenient and not wildly utilized. The choice of antihypertensive medication requires the clinician to take transplant and immunological factors into the consideration. Management for OSA and interventions for resistant HTN, such as transplant renal artery angioplasty ± stenting, bilateral native nephrectomy, and native RDN, remain options for resistant HTN in selected kidney transplant recipients. There is no conclusive BP target for this population and therapy targets need to be individualized. Further research to develop a stronger body of evidence for the pathogenesis of post-transplant HTN and guide clinicians on the appropriate BP measurement method, use of antihypertensive medications, surgical or procedural interventions, and establish BP targets for kidney transplant recipients.ET participated in designing the topics and detail of the manuscript, writing the manuscript, and preparing figures and tables. MM participated in the design of the topics, detail of the manuscript, and the editing of the manuscript. BH, UR, DD, HI, and AA participated in preparing and reviewing the manuscript. AF and RH participated in preparing, editing, and reviewing the manuscript. KK-Z participated in designing the topics and detail of the manuscript as well as preparing and reviewing the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Currently, serum creatinine and estimated glomerular filtration rate (eGFR) together with albuminuria or proteinuria are laboratory markers used in long-term monitoring of kidney transplant recipients. There is a need for more sensitive markers that could serve as early warning signs of graft dysfunction. Our aim was to assess the urinary concentrations of neutrophil gelatinase-associated lipocalin (NGAL) as a predictor of changes in kidney transplant function after the first year post-transplantation. We prospectively recruited 109 patients with functioning graft at least one year after the transplantation, with no acute conditions over the past three months, during their control visits in kidney transplant ambulatory. Urinary NGAL measured on recruitment was twice higher in patients with at least 10% decrease in eGFR over 1-year follow-up compared to those with stable or improving transplant function. Baseline NGAL significantly predicted the relative and absolute changes in eGFR and the mean eGFR during the follow-up independently of baseline eGFR and albuminuria. Moreover, baseline NGAL significantly predicted urinary tract infections during the follow-up, although the infections were not associated with decreasing eGFR. Additionally, we assessed urinary concentrations of matrix metalloproteinase 9—NGAL complex in a subgroup of 77 patients and found higher levels in patients who developed urinary tract infections during the follow-up but not in those with decreasing eGFR. High urinary NGAL in clinically stable kidney transplant recipients beyond the first year after transplantation may be interpreted as a warning and trigger the search for transient or chronic causes of graft dysfunction, or urinary tract infection.  Renal transplantation is the best therapeutic option for patients with end-stage kidney disease. Both donor—and recipient-related factors are associated with kidney graft function, including metabolic and immunological factors. Acute or chronic rejection, recurrent or de novo nephropathies, side effects of immunosuppressive drugs, comorbidities (including infections), and age-related decline in renal function adversely affect long-term survival of both kidney graft and transplant recipient. According to 2009 Kidney Disease: Improving Global Outcomes (KDIGO) guidelines , the monThe studies using protocol biopsies reveal the signs of chronic rejection in a significant proportion of cases without clinical signs of decreasing renal function ,4. StillIn the last 15 years, neutrophil gelatinase-associated lipocalin (NGAL) became one of the most extensively studied marker of acute kidney injury (AKI) ,10. NGALOur aim was to assess the concentrations of urinary NGAL with an automated laboratory method in kidney transplant recipients at least one year after transplantation and to study their association with changes in kidney function observed during one-year follow-up. Considering the intra-individual variability of serum creatinine and eGFR that is observed in clinical practice among chronic kidney disease patients, we compared the subgroups of patients with and without at least 10% decrease in eGFR over a 1-year follow-up. Additionally, we performed an exploratory analysis regarding the urinary concentrations of MMP 9-NGAL complex in a subgroup of studied patients.2, and no acute kidney injury fulfilling the definition of KDIGO 2011 [This was a prospective observational study. Patients were recruited in the ward dedicated to care of kidney transplant recipients, in the Chair and Department of Nephrology, University Hospital, Kraków, Poland between May and July 2019. The inclusion criteria were as follows: age of at least 18 years, at least one year from transplantation, functioning kidney transplant with eGFR at least 15 mL/min/1.73 mIGO 2011  or any cOn recruitment, patients signed an informed consent for the study. They underwent detailed history and physical examination. Urine and venous blood samples were collected for the laboratory tests in the morning of the day of the study visit. The baseline clinical data and the results of routine laboratory tests on enrollment were recorded. The data regarding transplantation procedure  and the primary cause of kidney disease were based on the available medical records. The data on pretransplant panel reactive antibodies (PRA) and donor/recipient human leukocyte antigens (HLA) mismatches were based on transplantation protocols available for the patients who had undergone transplantation procedure in University Hospital, Kraków, Poland. In September 2020, the follow-up data were collected based on medical records of the patients who remained in control in the kidney transplant recipients’ ambulatory, including the clinical course during the follow-up, the serum creatinine concentrations obtained during all control visits, and the results of laboratory tests performed at the last visit of a patient in the kidney transplant recipients’ ambulatory.The study protocol was approved by the Jagiellonian University Bioethical Committee .2EDTA-anticoagulated samples, biochemical and immunochemical tests , and urinalysis. In addition, urine protein, albumin, NGAL and creatinine concentrations were assessed in the samples obtained at the initial study visit. Excess serum and urine samples were aliquoted and frozen in −80 °C within 2 h from samples’ collection. Within two months, the thawed samples were centrifuged and the supernatant was analyzed for NGAL and MMP 9-NGAL complex. Urine NGAL was assessed with chemiluminescence microparticle immunoassay (Architect urine NGAL) on Abbott Architect analyzer . The limit of detection for the test was estimated for 0.7 ng/mL by the manufacturer; the intra- and inter-assay precision were ≤5.2% and ≤6.7%, respectively. The tests were performed in Diagnostic Department of Hospital University, Krakow, Poland, on the day of samples’ collection. MMP 9-NGAL complex was assessed in series in duplicate wells per sample using Quantikine ELISA Human MMP-9/NGAL Complex Immunoassay . The minimum detectable dose of human MMP 9-NGAL was 0.013 ng/mL. According to the manufacturer of the test, the mean urine concentrations in healthy volunteers was 0.44 ng/mL (ranged from non-detectable to 0.67 ng/mL). The measurements were performed in the Department of Diagnostics, Chair of Clinical Biochemistry, Jagiellonian University Medical College, Krakow, Poland.The blood and urine samples for laboratory tests were collected in the morning hours after an overnight fast. Routine laboratory test included complete blood count performed in Kp-value < 0.05. Statistica 12  and Statistica 13 software  were used for computation.The number of patients and the percentage of the respective group were reported for categories. The contingency tables were analyzed with Pearson’s chi-squared test. The mean ± standard deviation (SD) or median with lower and upper quartile  were reported for quantitative variables with or without normal distribution, respectively. The variables’ distributions were assessed for normality with the Shapiro-Wilk’s test. The groups were compared using t-test or Mann-Whitney’s test, depending on the variables’ distributions. Time-related changes were assessed with the Wilcoxon’s matched pairs test as the appropriate variables’ distributions differed from normal. Simple correlations were analyzed with the Pearson’s correlation coefficient, calculated using log-transformed variables in case of right-skewed distribution. Simple correlations between urinary NGAL, NGAL/creatinine and the number of mismatched HLA were analyzed with the Spearman rank coefficient. Multiple linear regression was used to identify the independent predictors of eGFR changes and eGFR based on mean creatinine during the follow-up period. The regression models included the independent variables that were significantly associated with at least one dependent variable in simple analysis, and were additionally adjusted for time from kidney transplantation (because of the considerable diversity of the time from transplantation in the studied group). Sex-adjusted logistic regression was used to assess the studied laboratory markers as the predictors of urinary tract infections during follow-up. Receiver operating characteristics (ROC) curve analysis was used to assess and compare the diagnostic accuracy of urine NGAL and albumin concentrations (raw and corrected to urine creatinine) for the prediction of at least 10% decrease in eGFR values over the follow-up period. The cut-off values were selected using maximum Youden index. All tests were two-tailed; the results were considered significant at We recruited 109 adult kidney transplant recipients . The patients were recruited in a single center, the Chair and Department of Nephrology, University Hospital in Kraków, Poland, during the control ambulatory visits. The time from transplantation ranged from 1 year to 22 years, with a median of 7 years. According to 2012 KDIGO guidelines on chronic kidney disease , there wThe follow-up data were collected during planned control visits over a period of up to 16 months from the enrollment. After a median 12.4-month observation , 10% or higher decrease in eGFR  was noted in 30 patients 28%; . The basUrinary albumin and albumin to creatinine ratio (uACR) were significantly higher in patients with ≥10% decrease in eGFR over a follow-up . Also, tp = 0.8; 2 . On the contrary, we observed a significant increase in eGFR values in the subgroup with final eGFR >90% of baseline eGFR .During the follow-up, we observed both increases and decreases in eGFR values . In the p = 0.2). The median eGFR based on mean creatinine during the follow-up period was 48  mL/min/1.73 m2 and was significantly lower among patients with ≥10% decrease in eGFR as compared to the rest of the group . Two of these patients progressed to stage G5 CKD and were referred to hemodialysis treatment. Further four patients were diagnosed with urinary tract infection, two with other infections, one with recurrent glomerulonephritis, two with cardiovascular complications, and one with adverse drug reaction that were recognized as resulting in a transient decrease of the transplant function. In the remaining 11 patients, there was no entry in their medical records about the (suspected) cause of eGFR decrease in medical records.p = 0.5) and NGAL to creatinine ratios  did not correlate with the baseline eGFR values either in the total cohort and in the subgroups defined by final to baseline eGFR ratio below or above 90% of the baseline value. Urine NGAL concentration and NGAL to creatinine ratio were significantly correlated with urine albumin and uACR at baseline . Urinary NGAL and NGAL/creatinine were not associated with age (p > 0.7), sex (p > 0.1), or time from transplantation (p > 0.5). Among the patients who had undergone transplantation procedure in our center, there was a marginally significant positive correlation between the urine NGAL concentration and the number of donor/recipient HLA mismatches . Other variables listed in The baseline urinary concentrations of NGAL . Neither the ratio of follow-up to baseline eGFR  nor the absolute difference between the follow-up and the baseline eGFR values  correlated with the length of observation. Also, neither the changes in eGFR nor mean follow-up eGFR were associated with sex.Baseline eGFR values, urinary albumin, and albumin to creatinine ratios, urinary NGAL and NGAL to creatinine ratios (but neither MMP 9-NGAL complex concentrations nor MMP 9-NGAl/creatinine ratios), as well as serum uric acid and albumin concentrations were significantly correlated with either the percentage or the absolute changes in eGFR values during the observation . Moreovep = 0.025 for final to baseline eGFR ratio as the dependent variable; −0.30 ± 0.10; p = 0.004 for final—baseline eGFR; and −0.12 ± 0.04; p = 0.005 for eGFR based on mean creatinine during the follow-up as the dependent variable, respectively). This results were observed despite the significant correlations of urinary NGAL concentration and NGAL/creatinine ratio with urine albumin and uACR.In multiple regression, urine NGAL and serum albumin were identified as the independent predictors of eGFR changes and eGFR values based on mean serum creatinine during the follow-up . When uAp = 0.7 in all comparisons). The cut-off values selected using maximum Youden index were 9.3 µg/L for urine NGAL concentration (associated with diagnostic sensitivity of 70% and specificity of 54%) and 24.1 µg/g for NGAL/creatinine (sensitivity 53% and specificity 76%), respectively.ROC curve analysis  showed ap = 0.035).We further analyzed the association between the baseline urinary NGAL and the changes in eGFR observed during the study in the subgroups of patients based on the time from transplantation: the correlations were weaker in the patients who were recruited between the end of the first and sixth year post-transplant as compared to those who had longer post-transplant history . Moreovep = 0.004). Eleven (52%) of the 21 patients were diagnosed with glomerular disease versus 28 (32%) in the rest of the group (p = 0.08). Age, time from transplantation, number of donor/recipient HLA mismatches, pretransplant PRA, the use of induction therapy, or transplant ischemia times did not differ between the groups. Persistent proteinuria was associated with higher decline in eGFR during the observation . The 21 patients with persistent or increased proteinuria were characterized by significantly higher baseline urine NGAL concentrations: median  23.0  versus 8.75  µg/L (p = 0.002) and NGAL/creatinine ratios: 35.1  versus 13.1  µg/g (p = 0.005).We analyzed the laboratory records of studied patients with respect to urine albumin or protein concentrations measured during the one-year follow-up. During the observation, proteinuria persisted or increased in 6 (15%) of 39 patients with A2 albuminuria and 15 (71%) of 21 patients with A3 albuminuria recorded at baseline. In the remaining patients, urine protein concentrations decreased during the observation. The patients with baseline uACR <30 mg/g did not develop increased proteinuria during the study. Among patients with persistent or increasing proteinuria, there were 6 (29%) recipients of second renal transplant, a significantly higher percentage as compared to the rest of the studied group . Also, eGFR values based on the mean serum creatinine during the follow-up did not differ between patients who developed urinary tract infections during the follow-up and those who did not .During the follow-up, bacterial urinary tract infections were diagnosed in 20 patients: four (14%) in the group that experienced ≥10% decrease in eGFR and 16 (20%) in the group with final eGFR >90% of initial value. The incidence of urinary tract infections did not differ significantly between the groups (p = 0.002) while they were not associated with diabetes (p = 0.6) or immunosuppressive treatment modality (p > 0.4). In logistic regression analysis, log-transformed urinary NGAL concentration  or log-transformed NGAL/creatinine ratio  predicted urinary tract infections during the follow-up independently of sex. On the contrary, urinary concentration of MMP 9-NGAL complex was significantly associated with sex  and did not prove sex-independent predictor of urinary tract infections. Urinary albumin and uACR were not associated with urinary tract infections during the follow-up (p = 0.3 for both comparisons).Baseline urine NGAL concentration, NGAL/creatinine ratio, MMP 9-NGAL complex and the complex to creatinine ratio were all significantly associated with bacterial urinary tract infections during the follow-up . The uriIn our sample of kidney transplant recipients recruited at least one year after the transplantation, without acute conditions diagnosed before and on enrollment, baseline urinary NGAL measured with the automated laboratory method significantly predicted the changes in eGFR values observed during the following year independently of other predictors, most importantly the baseline eGFR and albuminuria. Although the diagnostic accuracy of urine NGAL in the prediction of eGFR decline was low , it was statistically significant and did not differ significantly from the diagnostic accuracy of urine albumin. Higher baseline NGAL was also associated with persistent or increasing proteinuria during one-year observation of the studied patients. Moreover, higher baseline urinary NGAL and MMP 9-NGAL complex were observed in patients who developed urinary tract infections during the follow-up.2. Serum creatinine concentrations (and thus GFR estimate) is dependent of non-renal factors, e.g., water balance, nutritional status, physical exercise, other metabolic factors, or diet [2 per year is considered a rapid progression of chronic kidney disease [Although we recruited “clinically stable” patients, i.e., without any acute conditions (including infections and kidney injury) before and on enrollment, we observed significant changes in eGFR values during the follow-up: the final eGFR values were in the range of 40–170% of the initial values or −30 to +25 mL/min/1.73 m or diet . Togethe or diet . On the  disease . We beliAccording to the recent studies, chronic graft dysfunction is mainly caused by chronic antibody-mediated rejection, interstitial fibrosis, and tubular atrophy (IF/TA) induced by various chronic inflammatory processes, and BK polyoma virus (BKV) nephropathy. In protocol biopsies done in 1000 transplant recipients at 3, 12, 24, 48, and 60 months post-transplant, the signs of chronic rejection were detected in 17% of patients, and IF/TA in 30% . MoreoveMost studies evaluating urinary NGAL in kidney transplant recipients used NGAL concentrations measured early (hours till days) after transplantation procedure. Urinary NGAL measured between 6 and 48 h from the surgery predicted delayed graft function in most studies  ,39,40,41p = 0.06) higher NGAL as compared to transplant recipients with normal histology [We were able to identify only several reports where NGAL has been measured in kidney transplant recipients after the peri-transplantation period. Ramirez-Sandoval et al.  measuredistology . The resistology  show thaIn non-transplanted chronic kidney disease patients, higher urinary NGAL was associated with a chronic decline in kidney function ,44. MoreWhile the NGAL monomer has been associated with tubular injury, and neutrophils seem the main source of NGAL dimer in urine ,16,47, tIn our study, in addition to urinary NGAL, serum albumin and uric acid were also associated with the changes in eGFR and mean eGFR during the follow-up. Serum albumin is an indicator and predictor of poor nutritional status in kidney disease, moreover, it is a known negative acute phase protein ,54. The Our study has several limitations: first, although we included more than 100 patients, the decrease in kidney function was detected in below one third of them, resulting in limited number of such patients. Furthermore, the data on donor/recipient HLA mismatches and PRA were available in a subgroup of patients, and we were not able to report the data on donor-specific antibodies, as these started to be measured in Poland only recently. The causes of decline in transplant function were not verified in histopathological examination because the protocol biopsies are not practiced in our center, and because there were patients who did not agree to indication biopsy. A longer follow-up time would allow studying the association of baseline NGAL with subsequent graft loss, a more robust end-point as compared to the one chosen in our study. In our group only two patients started dialysis treatment due to the end-stage graft failure. However, it was our aim to seek for the predictors of less severe decline in transplant function.The strength of our study is that we measured urinary NGAL with a robust automated method that may be used in routine clinical practice (and indeed it is available in many centers). Although several studies show the diagnostic utility of urine NGAL for the prediction of adverse outcomes in kidney transplant recipients, the lack of standardization between the assays hinders the use of NGAL in clinical practice. We believe that the automated methods should be used in the studies if we want to translate the studies’ results into practice.In summary, our study indicates that the urinary NGAL and NGAL to creatinine ratio predicts changes in kidney graft function over subsequent year in kidney transplant recipients with long-term functioning graft. The association between urinary NGAL concentration and the follow-up graft function is moderate but independent of baseline eGFR and albuminuria. To which extent this prognostic utility of NGAL may be associated with the prediction of urinary tract infections, remains to be elucidated. Based on our observation, we may hypothesize that a high urinary NGAL measured as an additional marker in a clinically stable kidney transplant recipient should be interpreted as a warning sign, leading to detailed evaluation of a patient in search of either transient or chronic causes of graft dysfunction, or urinary tract infection. Low urinary NGAL is associated with a low risk of kidney graft dysfunction over a subsequent year. However, this clinical hypothesis must be verified in larger studies, at best involving the detailed characterization of graft state with the use of protocol biopsies.