Abstract
Some investigations, including ours, have previously reported that compared with normal subjects, both T3 and T4 levels in dialysis patients are significantly reduced, despite the patients being considered euthyroid, because serum basal TSH levels are maintained within normal range or at the upper limit of normal. Either FT3 or FT4 is reported to be exceedingly decreased. These findings often lead to confusion in evaluating the thyroid state of these patients. Recently, an abnormality of pulsatile TSH release was identified, which may provode evidence suggesting abnormal pituitary function. In addition to total T3 (TT3) and T4 (TT4), serum levels of total protein, albumin and TBG were decreased in these patients. Both FT3 and FT4 assayed by the analogue method (A), popular for measuring free thyroid hormones, were considerably reduced, whereas FT4 measured by the equilibrium dialysis method (E), a theoretically reasonable method, was within the normal range in the majority of patients (84%). (A) has some methodological problems in assessing the free hormone levels in serum, as several investigators have reported. The two methods may yield apparently discrepant values despite measuring the same hormone. TT4 correlated positively with the fall in TBG in a significant manner. TT3 correlated significantly with a reduction in serum albumin. FT3 and FT4, as assessed by (A), showed significant correlations with TBG. Mean serum selenium (Se) values in both HD and CAPD patients were much lower than in healthy controls. There was a strong positive correlation between TT3 and Se. The TT3/TT4 ratio, one of the markers of conversion from T4 to T3, also correlated with the Se level. Recently, it has been clarified that type I 5'-deiodinase is a selenoenzyme. These results are compatible with findings in Se-deficient rats. Our data suggest that FT4 in hemodialysis patients is normal and that a reduction in serum selenium appears to cause impairment of outer-ring deiodination of T4 in these patients.
