Radioimmunoassay of 3,3',5'-triiodothyronine (reverse T3) on small reusable sephadex columns

A simple radioimmunoassay for serum reverse triiodothyronine on small reusable Sephadex G 25 fine columns has been developed. The assay was unaffected by serum volumes of up to 100 microliter. The recovery of reverse T3 added to serum was in the mean 98.3 +/- SEM 3.2% and the coefficient of variation within and between assay determinations 5.4% and 7.5%, respectively. The detection limit was 2.2 pg reverse T3/column. Serum reverse T3 in 58 euthyroid controls was in mean 48 +/- SD 9 ng/100 ml, and was positively correlated to age (P less than 0.001). No overlap was found between the control group, and the hypo- and hyperthyroid group respectively. Three patients with T3-toxicosis had a normal serum rT3.