THE “EFFECTIVE THYROXINE RATIO” IN THE ASSESSMENT OF THYROID FUNCTION

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Abstract
A new commercial kit for the estimation of the “effective thyroxine ratio” (ETR) has been tested with 343 sera, and the results from patients with normal and abnormal thyroid functions have been compared with the results of the triiodothyronineresin uptake test and serum total thyroxine estimation. The ETR was found to be superior to these tests individually, and comparable in diagnostic accuracy with the “free thyroxine factor” derived from them together. This single procedure appears to reduce the frequency of misleading results that occur with both the resin uptake test and serum thyroxine estimation when alterations in thyroxine‐binding proteins are present—e.g., during pregnancy, or in the case of individuals on oral contraceptive therapy, or in the case of patients severely ill with non‐thyroid disorders. The ETR was also found to be as useful as the serum thyroxine estimation in assessing the adequacy of replacement thyroxine therapy and the response to the thyrotropin stimulation test.