Validity SPINA-GD correlates to the T4-T3 conversion rate in slow tissue pools, as determined with isotope-based measurements in healthy volunteers. It was also shown that GD correlates with resting energy expenditure, body mass index and thyrotropin levels in humans, and that it is reduced in nonthyroidal illness with hypodeiodination. Multiple studies demonstrated SPINA-GD to rise after initiation of substitution therapy with selenium, a trace element that is essential for the synthesis of<unk> . Clinical utility Compared to both healthy volunteers and subjects with hypothyroidism and hyperthyroidism, SPINA-GD is reduced in subacute thyroiditis. In this condition, it has a higher specificity, positive and negative likelihood ratio than serum concentrations of thyrotropin, free T4 or free T3. These measures of diagnostic utility are also high in nodular goitre, where SPINA-GD is elevated. Among subjects with subclinical thyrotoxicosis, calculated<unk> activity is significantly lower in exogenous thyrotoxicosis (resulting from therapy with levothyroxine) than in true hyperthyroidism (ensuing from toxic adenoma, toxic multinodular goitre or Graves' disease). SPINA-GD may therefore be an effective biomarker for the differential diagnosis of thyrotoxicosis. Compared to healthy subjects, SPINA-GD is significantly reduced in euthyroid sick syndrome. Pathophysiological and therapeutic implications Recent research revealed total<unk> activity to be higher in untreated hypothyroid patients as long as thyroid tissue is still present. This effect may ensue from the existence of an effective TSH-deiodinase axis or TSH-T3 shunt. After total thyroidectomy or high-dose radioiodine therapy (e.g. in treated thyroid cancer) as well as after initiation of substitution therapy with levothyroxine the activity of step-up<unk>  decreases and the correlation of SPINA-GD to thyrotropin concentration is lost. In two large population-based cohorts within the Study of Health in Pomerania SPINA-GD was positively correlated to some markers of body composition including body mass index (BMI), waist circumference, fat-free mass and body cell mass, confirming earlier observations in the NHANES dataset. This positive association was age-dependent and with respect to BMI significant in young subjects only, but with respect to body cell mass stronger in elderly persons. SPINA-GD is reduced in low-T3 syndrome and certain chronic diseases, e.g. chronic fatigue syndrome, chronic kidney disease, short bowel syndrome or geriatric asthma. In Graves' disease, SPINA-GD is initially elevated but decreases with antithyroid treatment in parallel to declining TSH receptor autoantibody titres. Although takotsubo syndrome (TTS) results in most cases from psychosocial stressors, thereby reflecting type 2 allostatic load, SPINA-GD has been described to be reduced in TTS. This may result from concomitant non-thyroidal illness syndrome, so that the clinical phenotype represents overlapping type 1 and type 2 allostatic response. In hyperthyroid men both SPINA-GT and SPINA-GD negatively correlate to erectile function, intercourse satisfaction, orgasmic function and sexual desire. Substitution with selenomethionine results in increased SPINA-GD in subjects with autoimmune thyroiditis. In subjects with diabetes SPINA-GD is positively correlated to several bone resorption markers including the N-mid fragment of osteocalcin and procollagen type I N-terminal propeptide (P1NP), as well as, however in men only, the β-C-terminal cross-linked telopeptides of type I collagen (β-CTX). Deiodination capacity proved to be an independent predictor of substitution dose in a trial with over 300 patients on replacement therapy with levothyroxine. Probably as a consequence of non-thyroidal illness syndrome, SPINA-GD predicts mortality in trauma and postoperative atrial fibrillation in patients undergoing cardiac surgery. Correlations were also shown to age, total atrial conduction time, and concentrations of 3,5-diiodothyronine and B-type natriuretic peptide. In a population suffering from pyogenic liver abscess SPINA-GD correlated to markers of malnutrition, inflammation and liver failure. A study on subjects with Parkinson's disease found SPINA-GD to be significantly decreased in tremor-dominant and mixed subtypes compared to the akinetic-rigid type. Endocrine disruptors may have pronounced effects on step-up<unk> , as suggested by positive correlation of SPINA-GD to urine concentrations of cadmium and phthalate metabolites and negative correlation to mercury and bisphenol A concentration.
Sum activity of peripheral deiodinases
Thyroid hormone binding ratio
Thyroid's secretory capacity
Heart-type fatty acid binding protein
Insulin index
Pharmacokinetics of testosterone
Fatty acid ratio in food
Trinder glucose activity test