Importance of specific reference values for evaluation of the deteriorating thyroid function in patients with end-stage renal disease on hemodialysis

Background/Aim: We evaluated the thyroid function in end-stage renal disease (ESRD) on maintenance hemodialysis. Material/Methods: Thyroid function and clinical hypothyroid score were evaluated in 145 ESRD patients. Results: Comparison of thyroid function between 127 ESRD patients, excluding 18 patients with suppressed or elevated serum TSH level, and age/sex-matched healthy controls (76 in midlife group aged under 65 and 51 in late-life group aged 65 or over) using a multivariate logistic regression analysis suggested significant difference (P < 0.0001), mainly in serum fT₄ level (P = 0.0099) and age (P = 0.0492), but not in serum fT₃ (not significant; ns), TSH (ns) level or fT₃/fT₄ ratio (ns). Serum fT₃ level and fT₃/fT₄ ratio were significantly lower (P < 0.001) in late-life group only in ESRD. Reference values calculated for midlife ESRD patients, such as 0.6-1.3 ng/dl for fT₄ compared with 0.8-1.7 ng/dl for healthy control, were helpful for the diagnosis of mild but definite hyperthyroidism in whom serum fT₄ level was 1.5 ng/dl. The prevalence of primary thyroid dysfunction, compared with the values for ESRD, was 0.7% for hyperthyroidism, 1.4% for overt hypothyroidism and 10.3% for subclinical hypothyroidism. Hypothyroid score was high among those with ESRD independent of thyroid dysfunction. Conclusions: Serum fT₄ level was markedly lower without a change in fT₃/fT₄ ratio in ESRD. This may suggest typical carbohydrate-sufficient non-thyroidal illness. The specific reference values for ESRD were useful to evaluate borderline thyroid dysfunction and to evaluate the prevalence of the patients with primary thyroid dysfunction in ESRD.