Thyroid function in hemodialysis (HD) patients is generally considered to be normal in spite of low serum thyroid hormone levels. It is well known that assay of free T
4 (FT
4) by conventional RIA based on labelled T
4 analogue (AN-RIA) shows relatively low levels because of interference by serum proteins, such as albumin and T
4 binding globulin (TBG), in HD patients. In this study, we examined FT
4 levels in HD patients using a newly developed equilibrium dialysis radioimmunoassay (ED-RIA), and made a comparison with AN-RIA.
Serum FT
4 levels in 32 patients with chronic renal failure just before the first HD, 118 patients on maintenance HD and 43 normal healthy controls were assessed by AN-RIA and ED-RIA. By AN-RIA, 16 out of 32 patients (50%) just before the first HD and 34 out of 118 (29%) on maintenance HD were within normal range. However, by ED-RIA, 29 out of 32 (91%) and 98 out of 118 (83%) were within normal range, respectively. There was no significant correlation between FT
4 by ED-RIA and either serum albumin or TBG. There was a good correlation between ED-RIA and AN-RIA (r=0.636). We also measured FT
4 in HD patients with permanent or transient hypothyroidism due to Hashimoto's thyroiditis or iodine excess. The values by ED-RIA yielded reasonable results reflecting TSH secretion and clinical course. In conclusion, ED-RIA is very useful for measuring serum FT
4 in the assessment and monitoring of thyroid function during the clinical course in HD patients.
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