NOMURA, T., SAKURADA, T. YOSHIDA K., YONEMITSU, K., ITAGAKI, Y., SUZUKI, M., FUKAZAWA, H., KAISE, N., KAISE, K., YAMAMOTO, M., SAITO, S. and YOSHINAGA, K.
Determination of Free Triiodothyronine in Serum: Comparison of Radioimmunoassay with Equilibrium Dialysis Method. Tohoku J. exp. Med., 1985,
146 (3), 289-301-In normal volunteers, serum free triiodothyronine (FT
3) concentrations determined by Immophase FT
3 RIA kit, Amerlex FT
3 RIA kit and equilibrium dialysis methods (absolute FT
3, AFT
3: product of total T
3 and percent FT
3) were 4.03±0.65, 3.69±0.58 and 3.22±0.65pg/ml (mean±S.D.), respectively. The normal free triiodothyronine index (FT
3I) was 38.4±6.5. In patients with hyper-and hypothyroidism, the FT
3 values measured by these methods were clearly abnormal. In patients with decreased thyroxine binding-globulin, the mean FT
3 concentrations determined by these methods were not significantly different from the normal. However, the mean FT
3I was significantly lower than normal. In pregnant women at delivery, Amerlex FT
3 values were subnormal in 7 of 9 subjects. All of these samples except one were within the normal range when evaluated by Immophase FT
3 and AFT
3, although their mean values were significantly lower than the mean of normal. On the other hand, the mean FT
3I was not significantly different from the mean of normal. The correlations between FT
3 values estimated by different methods and between FT
3 values and FT
3I were all statistically significant. In a clinically euthyroid patient who had chronic thyroiditis and who was shown to have anti-T
3 antibody in her serum, Immophase FT
3 and Amerlex FT
3 values were above the high standards. However, AFT
3, calculated by multiplying total T
3 (determined after ethanol extraction) by percent FT
3 was normal. In conclusion, the evaluation of FT
3 by these radioimmunoassay methods proved clinically useful, when appropriate limitations are considered.
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