Closer correlation between serum triiodothyronine and basal metabolic rate during antithyroid drug treatment in patients with Graves' disease.

The correlations between serum triidothyronine (T3), thyroxine (T4), 131I-triiodothyronine resin sponge uptake (RT3U) or free thyroxine index (T7) and the basal metabolic rate (BMR) during antithyroid drug treatment in 86 patients with Graves' disease were investigated. Although serum T3, T4, RT3U and T7 during therapy with MMI showed significant positive correlations with BMR, the coefficient of correlation (r = 0.6088, P less than 0.001) between T3 and BMR was the highest of all. While the normal range of BMR in control subjects was between -1.9 and +14.9 (the range of mean +/- SD), the corresponding values of T3, T4, RT3U and T7 calculated from the regression lines, ranged from 94.2 to 184.0 ng/dl, from 5.32 to 8.75 microgram/dl, from 26.5 to 28.9% and from 1.57 to 2.47 respectively. On the other hand, when the corresponding values of BMR to normal values of T3 (100-170 ng/dl), T4 (7.6-12.2 microgram/dl), RT3U (26.7-36.5% and T7 (2.29-3.49) in control subjects were calculated from the regression lines, the range of value obtained from the regression line of T3 coincided better with normal value of BMR in control subjects that those calculated from other regression lines (T4, RT3U and T7). These results suggest that serum T3 level would be a better index of evaluation of the thyroid function that T4 or RT3U in patients with Graves' disease under antithyroid drug treatment.