ABSTRACT
There is a proportionally greater increase in the serum T3 than Serum T4 concentration in patients with hyperthyroidism due to Grave's disease which results in an elevation of serum T3 to T4 ratio. The study was undertaken to investigate the alteration of serum T3 to T4 ratio in relation to the outcome of antithyroid drug therapy. 98 patients of hyperthyroid Grave's disease were studied and 78 patients had T3 to T4 ratio greater than 20 ng/microgram before therapy (normal range 14-20; mean 16.0) In 16 out of 78 patient T3 to T4 ratio remained high during a 18 months course of antithyroid drug therapy and in 13 of them (81%) hyperthyroidism recurred after stoppage of treatment. In the remaining 62 patients, the initial high T3 to T4 ratio became normal (< 20) during treatment and 34 of them (54.9%) had a remission of the disease after stoppage of the drug. Of the 20 patients in whom the initial T3 to T4 ratios were within normal range, the ratio remained normal during treatment and 16(80%) had a remission. Goiter size was larger in patients with high serum T3 to T4 ratio and reduction of goiter size occurred in some patients (59%) with decreasing T3 to T4 ratios. It is concluded that serum T3 to T4 ratio is a single and a useful predictor of the outcome of antithyroid drug therapy in patients with hyperthyroidism due to Grave's disease. A ratio greater than 20 throughout therapy indicates that the chances of relapse is high and a ratio below 20 either initially or during therapy is an indication of prolonged remission.