T4, T3 and reverse-T3 determinations in connection with the TRH test in the evaluation of possible hyperthyroidism

One disadvantage of the TRH test is that an absent or blunted TSH response is seen not only in hyperthyroid patients but also in some normal subjects. The aim of the present study was to elucidate whether the discriminatory power between eu- and hyperthyroidism could be increased by determining the T3 and T4 levels before and after the TRH administration. The study population consists of 30 patients referred for evaluation of suspected hyperthyroidism. The results show that all but one of the patients (n=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. All the patients (n=10) who had T3 levels within the hyperthyroid range showed a decrease after TRH. The decrease was significantly correlated (r=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.