MEASUREMENT OF SERUM 3,3‘,5’-(REVERSE) T3, WITH COMMENTS ON ITS DERIVATION

Publisher Website
Google Scholar
Abstract
A radioimmunoassay for the measurement of L-3,3'',5''-triiodothyronine (reverse T3, rT3) was developed for use with unextracted serum. The highly specific antiserum showed no cross-reactivity with L-3,3''5-triiodothyronine (T3) or tetraiodothyroacetic acid (T4A) and cross-reaction with L-thyroxine (T4) was low enough to be discounted for routine assay purposes. If a normal amount of rT3 was added to serum T4 cross-reactivity decreased considerably. Serial dilutions of hyperthyroid sera gave dose-response curves which were parallel to the rT3 standard curve. Serum concentrations of rT3 (mean .+-. SEM) were 0.68 .+-. 0.02 nmol/l in 67 normal subjects, 0.19 .+-. 0.02 nmol/l in 12 hypothyroid patients and 1.18 .+-. 0.12 nmol/l in 17 hyperthyroid patients. In 16 patients with T3-toxicosis rT3 was 0.42 .+-. 0.04 nmol/l, and 18 patients with high circulating TBG [thyroxine binding globulin capacity] had a mean rT3 of 0.54 .+-. 0.03 nmol/l.