FREE-THYROXINE CONCENTRATIONS IN SERUM MEASURED BY EQUILIBRIUM DIALYSIS IN CHRONIC-RENAL-FAILURE

The serum concentration of free thyroxine (FT4) is often low in patien ts with chronic renal failure (CRF) with low serum concentrations of t riiodothyronine (T-3). We evaluated the serum FT4 concentration by usi ng both an equilibrium dialysis RIA kit (D-FT4) and a labeled-antibody kit (M-FT4) in two different groups of CRF patients, undergoing chron ic hemodialysis (HD, n = 145) or not (non-HD, n = 30), and in a group of normal healthy subjects (n = 58). Thyroid peroxidase antibodies and thyroglobulin antibodies were not detected in any patient. Serum FT4 concentrations (mean +/- SD, pmol/L) by the D- and M-FT4 assays were, respectively, 21.5 +/- 4.6 and 16.6 +/- 2.0 in the healthy subjects, 1 7.8 +/- 4.3 and 13.9 +/- 3.6 in the non-HD patients, and 16.9 +/- 4.9 and 10.7 +/- 1.9 in the HD patients. By the D-FT4 assay, results for b oth CRF groups n ere significantly different from those for the health y group (P < 0.01), as were the results for each pair of groups by the M-FT4 assay (P < 0.01). FT4 values were reported as being within the healthy reference range by D-FT4 in 73 of 113 HD subjects who had low T-3 and low M-FT4 values. Serum FT4 concentrations measured by both as say kits showed a significant inverse correlation with the serum conce ntration of creatinine (P < 0.01), but the serum concentrations of sex -hormone-binding globulin did not differ significantly among the three groups, Our results indicate that the low FT4 concentration measured by D-FT4 in patients with CRF, particularly those on HD, probably refl ects the actual, mild nonthyroidal illness of renal failure.