QUANTITATIVE OBSERVATIONS WITH THE TRIIODOTHYRONINE SUPPRESSION TEST OF THYROID FUNCTION*

Triiodothyronine (T3), 120 to 150 μg. per day, was administered for seven days to 50 thyrotoxic patients and 109 euthyroid subjects. The thyroidal I131 uptake rate was determined before and during administration of T3. Diagnostic borderlines were determined by analysis of the ratios of these uptake rates. The triiodothyronine suppression test is a useful diagnostic aid, and is the suppression test of choice. Diagnostic data are obtained sooner and are less likely to be affected by prior antithyroid medication than with the thyroxine suppression test.