Serum thyroxine, serum % -- T3 -- binding, and serum T3 in Zambians.

Serum total thyroxine (T4) was measured in clinically euthyroid and clinically hyperthyroid subjects, using the method of competitive protein binding. In 26 euthyroid subjects the mean +/- 1SD was 7.7 +/- 1.8 micrograms/dl and in 17 clinically hyperthyroid subjects, the mean +/- 1SD was 18.1 +/- 3.1 micrograms/dl. This difference is statistically significant. Serum % 125(1) -- T3 binding was measured using the principle of competition for 125(1) -- T3 between the unknown serum and the resin in the assay kit. In 18 clinically euthyroid subjects, the mean +/- 1SD was 112.6 +/- 4.4 % while in 14 clinically hyperthyroid subjects the % 125(1) -- T3 binding had a mean +/- 1SD of 71.4 +/- 11%. The difference is statistically significant. Serum total triiodothyronine was measured by radioimmunoassay. In 31 clinically euthyroid subjects the mean +/- 1SD was 146 +/- 19.8 ng/dl while in 19 clinically hyperthyroid sugjects the mean +/- 1SD was 390 +/- 111 ng/dl. This difference is statistically significant. There was a negative correlation which was not statistically significant between the serum T4 and % T3 binding. The measurements of these thyroid function indices were precise.