cardiovascular disease ( cvd ) including sudden cardiac death ( scd )   is a major cause of mortality in chronic kidney disease ( ckd ) . apart from left ventricular dysfunction , unique factors such as autonomic imbalance and inflammation contribute to the high incidence of scd in ckd . traditional risk factors for atherosclerosis , such as hypertension and dyslipidaemia , can to some extent explain the increased risk of atherosclerosis in ckd . however , nontraditional risk factors like oxidative stress and inflammation may also be of importance . heart rate variability ( hrv ) is a reliable , noninvasive measurement of autonomic tone of the heart . a reduction in hrv reflects an autonomic imbalance towards decreased vagal tone and subsequent sympathetic overactivity . chronic , low - grade inflammation is involved in the development of both scd   and atherosclerosis . the most extensively examined marker of inflammation is high - sensitive c - reactive protein ( hs - crp ) , which is a predictor of cardiovascular mortality in different populations [ 12 , 13 ] including patients with ckd . hs - crp may even be a risk marker for scd [ 10 , 15 ] . haptoglobin ( hp ) is an abundant acute - phase protein as well as an innate antioxidant involved in the scavenging of free haemoglobin . thus , hp prevents iron - mediated formation of free reactive oxygen species known to initiate oxidative stress . in humans , hp is characterised by molecular heterogeneity with three common genotypes : 1 - 1 , 2 - 2 , and 2 - 1 . the antioxidant ability of hp is genotype dependent with hp 2 - 2 being the weakest antioxidant . there is evidence establishing hp 2 - 2 as a predictor of cvd in diabetes mellitus [ 20 , 21 ] . however , results are inconsistent regarding hp genotypes and cardiovascular mortality in patients with ckd [ 22 , 23 ] . a study in patients with ischemic heart disease ( ihd ) revealed a positive association between low hrv and hp 2 - 2 . the aim of the present study was to determine whether hp genotype was associated with the cardiovascular risk markers hrv and hs - crp in patients with ckd . sixty - four patients from the outpatient clinic at the department of nephrology , aalborg hospital , denmark , were included . exclusion criteria were the start of dialysis within three months , nephrotic syndrome , malignancy , uncontrolled hypertension , or a previous renal transplantation . patients were also excluded if they had an ongoing infection , a myocardial infarction during the last six months , or supraventricular arrhythmia . the causes of ckd were chronic glomerulonephritis ( 32% ) , hypertensive nephropathy ( 23% ) , polycystic kidney disease ( 13% ) , and other causes including interstitial nephritis and chronic pyelonephritis ( 32% ) . the study was conducted in accordance with danish legislation and the declaration of helsinki and approved by research ethics committee of the north denmark region . creatinine clearance was calculated using a 24  h urine collection and a blood sample for serum creatinine . hs - crp was measured using an advia 1650 analyzer ( bayer corp . , pittsburgh , pa , usa ) and an immunoturbidimetric assay ( randox laboratories ltd . , antrim , uk ) . the hp genotype was determined by high - performance liquid chromatography as previously described , using a superdex 200 hr 10/30 column for chromatographic separation ( amersham pharmacia biotech ab , birkerd , denmark ) . phosphate - buffered saline ( 50  mmol / l sodium phosphate , 150  mmol / l sodium chloride , and 0.01% sodium azide ; ph 7.3 ) was used as the mobile phase . flow rate was 1  ml / min ( 76.4  cm / hour ) . hp genotype was determined from the curve shape and relative retention time of the chromatograms . a 24  h holter recording was obtained on a flash card using a 3-channel digital monitor dl-700 ( diagnostic monitoring , santa ana , ca , usa ) , and time domain variables were analysed using commercially available software ( diagnostic monitoring , santa ana , ca , usa ) . if more than 20% of qrs complexes were abnormal or of poor technical quality , the analysis was excluded in the overall hrv analysis . the time domain variables were identified as follows : ( 1 ) mean of all normal - to - normal rr intervals , ( 2 ) standard deviation ( sd ) of all normal - to - normal rr intervals ( sdnn ) , ( 3 ) mean of the sds of all normal - to - normal rr intervals ( sdnnindex ) , ( 4 ) sd of the mean normal - to - normal rr intervals for each 5-minute period ( sdann ) , ( 5 ) percentage of successive rr interval differences > 50  ms ( pnn50 ) , and ( 6 ) square root of the mean of the sum of squares of differences between adjacent rr intervals ( rmssd ) . blood pressure was obtained with a 24  h ambulatory bp device , tm 2412 ( a&d co. ltd . , tokyo , japan ) . for analysis , the statistical analysis was performed using stata software , version 10 ( statacorp lp , tx , usa ) . the hp alleles were tested for hardy - weinberg equilibrium using an asymptotic hardy - weinberg equilibrium test .   for the comparison of sdnn , sdann , and hs - crp , respectively , between the three common hp genotypes , crude one - way analysis of variance was performed . data was divided into two groups according to the presence of the hp allele 1 : one group including hp 1 - 1 and hp 2 - 1 patients and the remaining group consisting of hp 2 - 2 patients . for comparisons of groups , student 's t - test was used for continuous variables and fisher 's exact test for categorical variables . linear regression was used to analyse the effect of hp 2 - 2 compared to hp 1 - 1 and hp 2 - 1 on sdnn , sdann , and hs - crp , respectively . the analyses were performed with the hp group as the independent variable and sdnn , sdann , and hs - crp , respectively , as the dependent variables . adjustments for potential confounders described in previous studies ( age , gender , heart rate , beta - blocker treatment , and creatinine clearance for hrv indices and age , gender , body mass index , and smoking status for hs - crp ) [ 2628 ] were performed . the frequencies of the three common genotypes were hp 1 - 1 21% , hp 2 - 1 50% , and hp 2 - 2 29% , and the hp allele frequencies ( hp allele 1 0.457 and hp allele 2 0.544 ) were in hardy - weinberg equilibrium (  = 2.07 and p = 0.1 ) . the genotype frequencies in the cohort were similar to those reported previously in northwestern european countries (  = 3.42 and p = 0.2 )   and similar to those reported previously in a danish population (  = 3.40 and p = 0.2 ) . figure 1 depicts mean sdnn and sdann , and figure 2 mean hs - crp in the three common hp genotypes . no differences were demonstrated between hp 1 - 1 and hp 2 - 1 regarding sdnn , sdann , and hs - crp , respectively . however , significant differences were observed between hp 1 - 1 and hp 2 - 2 and between hp 2 - 1 and hp 2 - 2 for both sdnn and hs - crp . however , for sdann , a significant difference was demonstrated only between hp 2 - 1 and hp 2 - 2 . table 1 shows clinical characteristics in the hp genotypes divided into two groups according to the presence of hp allele 1 . the two groups were generally comparable , although there were fewer women in the hp 2 - 2 group . sdnn and sdann were significantly lower in the hp 2 - 2 patients compared to the hp 1 - 1 and hp 2 - 1 patients ( table 1 ) . the other time domain indices rr , sdnnindex , pnn50 , and rmssd showed a similar trend although not statistically significant . multivariate linear regression analyses of hp 2 - 2 and sdnn and sdann , respectively , were performed adjusting for previously described confounders . hp 2 - 2 was negatively and independently associated with both sdnn and sdann ( table 2 ) . apart from hp 2 - 2 , the strongest determinants of sdnn in the model were age ( p < 0.001 ) and heart rate ( p = 0.04 ) , and the strongest determinants of sdann were age ( p < 0.001 ) , heart rate ( p = 0.05 ) , and beta - blocker treatment ( p = 0.04 ) . after adjusting for age , gender , heart rate , creatinine clearance , and beta - blocker treatment , hp 2 - 2 was still significantly associated with both sdnn and sdann . levels of hs - crp were significantly higher in the hp 2 - 2 patients compared to the hp 1 - 1 and hp 2 - 1 patients ( table 1 ) . in the multiple linear regression analysis of hs - crp and hp 2 - 2 ( table 2 ) , adjustments were made for confounders known from previous studies [ 27 , 28 ] . only hp 2 - 2 revealed a positive and significant association with hs - crp in the model . the present study demonstrated a close association between hp genotype and the cardiovascular risk markers hrv and hs - crp in patients with ckd . thus , patients with hp 2 - 2 had significantly lower hrv and higher levels of hs - crp . establishes an scd as one of the most single important causes of death in patients with ckd . well - described risk factors of scd in the general population also apply to patients with ckd . however , several unique factors such as autonomic imbalance and inflammation are recognized . hrv is being increasingly used as a valid and easily obtainable prognostic marker of autonomic alterations . as reviewed by ranpuria et al . , hrv is a promising surrogate marker for scd in patients with ckd and a potential modifiable outcome measure .   in haemodialysis patients , oikawa et al . found decreased sdnn to be a predictor of all - cause and cardiovascular mortality . recently , chandra et al . studied hrv in patients with ckd stage 35 demonstrating that lower hrv was independently associated with higher risk of cvd and mortality . christensen et al . has previously addressed the issue of a possible association between hrv and hp genotype . in patients with ihd , a significant association between time domain variable rmssd and hp 2 - 2 was shown . the present study did not show an association between rmssd and hp 2 - 2 . however , a highly significant association between hp 2 - 2 and sdnn and sdann , primarily reflecting circadian rhythm and long - term fluctuations , was demonstrated . a relationship between the autonomic nervous system and inflammation has been established showing increase in vagal tone as a counter - response to cytokine synthesis . tracey   first described this cholinergic anti - inflammatory pathway as a plausible , molecular mechanism for the association between hrv and hs - crp . in a cohort of patients with ckd , psychari et al . demonstrated a negative association between inflammatory marker interleukin-6 and sdnn and sdann , respectively furthermore , in a large cohort of end - stage renal disease patients , parekh et al .   found a positive association between hs - crp and scd , independently of other known cardiovascular risk factors . direct effects on the vagal conduction system and resulting aggravation of sympathetic tone may contribute to the increased risk of scd . being the weaker antioxidant of the three common hp genotypes , hp 2 - 2 may be unable to hinder oxidative damage to the autonomic nervous system , especially in patients with ckd exposed to a prooxidative milieu due to uremic toxins . studies have established hp 2 - 2 as a potential risk predictor of cvd in patients without ckd . chapelle et al .   showed that more extensive myocardial infarction occurred in hp 2 - 2 patients . demonstrated that hp 2 - 2 patient undergoing coronary bypass surgery needed more grafts and had shorter graft survival time . on the contrary , in a nested control study de bacquer et al . showed that hp 1 - 1 patients had a higher risk of ihd compared to hp 2 - 2 and hp 2 - 1 patients . studies on cvd and hp genotype in diabetes show more consistent results , both in human studies   and recently in a mouse model . levy et al . demonstrated in the strong heart study   that hp 2 - 2 is a major predictor of cvd in patients with diabetes . yet , in a cross - sectional study of the framingham offspring cohort , levy et al . found that hp 2 - 2 and hp 2 - 1 patients with diabetes had decreased cvd prevalence . a possible relation between hs - crp and hp 2 - 2 has been examined in several studies . in patients with peripheral occlusive disease , delanghe et al .   found a higher , yet statistically insignificant , hs - crp in hp 2 - 2 patients compared to hp 1 - 1 and hp 2 - 1 patient . likewise , braeckman et al .   found a higher , but also statistically insignificant , hs - crp in apparently healthy hp 2 - 2 individuals compared to hp 1 - 1 and hp 2 - 1 individuals . however , delanghe et al . demonstrated in patients with essential hypertension higher hs - crp in hp 2 - 2 patients . the present study establishes a potential role for hp 2 - 2 as a risk predictor of cvd in patients with ckd through an association with hs - crp . numerous studies have documented hs - crp to be a valid and well - documented marker of inflammation   and hence a predictor of atherosclerosis and cardiovascular mortality in patients with ihd   as well as in patients with ckd , as recently demonstrated by bazeley et al . .   in patients with ckd pernod et al . found a prevalence of hp 2 - 2 twice as high in end - stage renal disease patients with high cvd risk , defined as prior cardiovascular event , diabetes , or dyslipidemia , compared to end - stage renal disease patients with low cvd risk . in a group of end - stage renal disease patients with diabetes , burbea et al .   found a survival advantage in hp 1 - 1 patients above 60 years , whereas patients below 60 years demonstrated a better survival when having hp 2 - 2 . however , pernod et al . found no association between hp genotype and cardiovascular mortality in patients with end - stage renal disease . lipid oxidation plays a crucial role in the initiation of atherosclerosis , and the first step in lipid oxidation is mediated by redox - active metals such as iron . brouwers et al . demonstrated that hp 2 - 2 is associated with high circulating levels of oxidised low - density lipoprotein thus posing a potential proatherogenic pathway for hp 2 - 2 . in an animal model of knock - in hp 2 - 2 mice , levy et al . demonstrated that hp contributes to atherosclerotic plaque modulation by increasing the local inflammation . hp 2 - 2 plaques accumulate more macrophages and have decreased levels of antiinflammatory cytokines . furthermore , hp 2 - 2 has been associated with diminished nitric oxide bioavailability [ 50 , 51 ] , a crucial step in endothelial dysfunction and hence initiation of atherosclerosis . furthermore , the underlying renal disease pattern is divers and comprises diseases with both high and low levels of inflammation . the design of the study is cross - sectional potentiating a risk of bias , and the causal inference can not be established . in conclusion , in patients with ckd , a negative association was observed between hp 2 - 2 and hrv . thus , hp 2 - 2 may indicate a poor outcome in patients with ckd , and one may speculate that hp 2 - 2 can help predict cardiovascular risk in patients with ckd as previously demonstrated in patients with diabetes .