T4, T3 and Reverse‐T3 Determinations in Connection with the TRH test in the Evaluation of Possible Hyperthyroidism

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Abstract
One disadvantage of the TRH [thyrotropin releasing hormone] test is that an absent or blunted TSH [thyrotropin] response is seen both in hyperthyroid patients and in some normal subjects. Whether the discriminatory power between eu- and hyperthyroidism could be increased by determining the T3 [triiodothyronine] and T4 [thyroxine] levels before and after the TRH administration was investigated. The study population consists of 30 patients referred for evaluation of suspected hyperthyroidism. The results show that all but 1 patient (20) who had T3 levels within the normal reference limits increased these levels after TRH administration whether their TSH response was normal or blunted. One patient''s T3 levels decreased after TRH. Patients (10) who had T3 levels within the hyperthyroid range showed a decrease after TRH. The decrease was significantly correlated (r [correlation coefficient] = 0.90) to the magnitude of the increase. No consistent T4 and no change in reverse-T3 response was obtained. The addition of T3, T4 or reverse-T3 determinations in connection with the TRH test does not seem to increase the discriminatory power of the test.