Rapid simultaneous radioimmunoassay for the measurement of triiodothyronine and thyroxine in unextracted human serum.

A rapid simultaneous radioimmunoassay for the measurement of triiodothyronine and thyroxine in unextracted human serum is described. The method requires 25 mul serum. Approximately 150 human sera can be tested for triiodothyronine and thyroxine levels in one day by one technical assistant. The triiodothyronine levels in peripheral venous blood in euthyroid subjects and in patients with various thyroid diseases are as follows: euthyroid (50) 115 +/- 22 (mean +/- SD) ng/100 ml, hypothyroid (20) 33 +/- 35 (mean +/- SD) ng/100 ml and hyperthyroid (20) 411 +/- 142 (mean +/- SD) ng/100 ml. The corresponding levels for thyroxine are: 6.9 +/- 1.3, 2.0 +/- 1.4 and 21.4 +/- 5.2 mug/100 ml. The levels of triiodothyronine in the thyroid venous blood are higher (P less than 0.05) than in the peripheral venous blood. The levels of thyroxine in the thyroid venous blood was not significantly higher than in peripheral venous blood.