Determination of free triiodothyronine in serum: comparison of radioimmunoassay with equilibrium dialysis method.
In normal volunteers, serum free triiodothyronine (FT3) concentrations determined by Immophase FT3 RIA kit, Amerlex FT3 RIA kit and equilibrium dialysis methods (absolute FT3, AFT3: product of total T3 and percent FT3) were 4.03 +/- 0.65, 3.69 +/- 0.58 and 3.22 +/- 0.65 pg/ml (mean +/- S.D.), respectively. The normal free triiodothyronine index (FT3I) was 38.4 +/- 6.5. In patients with hyper-and hypothyroidism, the FT3 values measured by these methods were clearly abnormal. In patients with decreased thyroxine binding-globulin, the mean FT3 concentrations determined by these methods were not significantly different from the normal. However, the mean FT3I was significantly lower than normal. In pregnant women at delivery, Amerlex FT3 values were subnormal in 7 of 9 subjects. All of these samples except one were within the normal range when evaluated by Immophase FT3 and AFT3, although their mean values were significantly lower than the mean of normal. On the other hand, the mean FT3I was not significantly different from the mean of normal. The correlations between FT3 were all statistically significant. In a clinically euthyroid patient who had chronic thyroiditis and who was shown to have anti-T3 antibody in her serum, Immophase FT3 and Amerlex FT3 values were above the high standards. However, AFT3, calculated by multiplying total T3 (determined after ethanol extraction) by percent FT3 was normal. In conclusion, the evaluation of FT3 by these radioimmunoassay methods proved clinically useful, when appropriate limitations are considered.
D003956:Dialysis / Q000379:methods; D005069:Evaluation Studies as Topic; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood; D007037:Hypothyroidism / Q000097:blood; D011863:Radioimmunoassay / Q000379:methods; D011933:Reagent Kits, Diagnostic; D012016:Reference Values; D013975:Thyroxine-Binding Proteins / Q000032:analysis; D014284:Triiodothyronine / Q000097:blood*
D011933:Reagent Kits, Diagnostic; D013975:Thyroxine-Binding Proteins; D014284:Triiodothyronine