SERUM FREE TRIIODOTHYRONINE TO FREE-THYROXINE RATIO ENABLES EARLY PREDICTION OF THE OUTCOME OF ANTITHYROID DRUG-THERAPY IN PATIENTS WITH GRAVES HYPERTHYROIDISM

This study scrutinizes the correlation between serum free triiodothyro nine (FT3) to free thyroxine (FT4) ratios and the eventual outcome of antithyroid drug (ATD) therapy in patients with Graves' disease. Forty -four patients with Graves' thyrotoxicosis were treated with methylmer captoimidazole (methimazole). During the follow-up, 16 patients relaps ed in the short period of one to five months after cessation of the dr ug (relapse group), and 28 patients remained in remission when checked at 12 to 20 months after treatment (remission group). Serum FT3 to FT 4 ratios [(pg/ml/ng/dl) x 10] were less than 55 throughout ATD therapy in 27 of the 28 remission patients whereas the ratios of the relapse group exceeded 55 from the early phase of methimazole treatment in 10 of 16 patients. In eight of these 10 patients the increased ratios wer e detected within three months of therapy (1 month, 3 patients; 2 mont hs, 4 patients; 3 months, 1 patient). The ratios for the remaining two patients rose above 55 at the fifth and sixth months. There was no st atistical difference between the remission and relapse groups in the F T3 to FT4 ratios either before nor at the completion of the treatment. However, a clear difference could be measured at a point during the t herapy. Those in whom this difference was pronounced later underwent r elapse. It was therefore concluded that scrutiny of the serum FT3 to F T4 ratio could be a simple and effective method predicting the outcome of antithyroid drug therapy in patients with Graves' disease and furt hermore that this ratio could indicate the likelihood of relapse as ea rly as within three months of methimazole treatment, thus saving sever al months of patients' and clinicians' time and, when necessary, allow ing for early implementation of an alternative therapy.