Different sensitivity of 131I uptake and TRH test during thyroxine treatment of nontoxic goiter.

Abstract

Three groups of patients with nontoxic goiter were treated with T4 and studied serially. The first group (54 cases) was treated with 50 μg/day for the first month, 100 μ/day for the second, 150 μg/day for the third, and 200 μg/day for the fourth. The 4- and 24-h thyroidal 131I uptake, serum T4, resin T3 uptake, and serum TSH before and 30 min after the iv injection of 200 μg TRH were measured before and after each treatment period. The TRH response was suppressed with smaller doses of T4 than the 131I uptake. Using as the criterion for TSH suppression a completely absent TRH response and as the criterion for 131I suppression a 24-h 131I uptake of ≦5% of the administered dose, the proportion of patients showing a suppression by the TRH and the 131I tests respectively, were: with 50 μg/day, 28.5% for TRH and 0% for 131I uptake; with 100 μg/day, 70% for TRH and 7.5% for 131I uptake; with 150 μg/day, 87.5% for TRH and 22.5% for 131I uptake; and with 200 μg/day, 100% for TRH and 54.2% for 131I uptake. All diff...