Simplified radioimmunoassay for triiodothyronine: evaluation of a new commercial kit

Abstract

A new triiodothyronine (T3) radioimmunoassay kit offers simplicity of method, short incubation time, specificity, and reproducibility. 125I labeled T3 and unknown serum (or standard) are added to alkaline buffered (pH 12.4) Sephadex G 25 columns; the T3 is freed of proteins with an alkaline buffer wash, antiserum is added, and the columns are incubated at room temperature for 2 h. 'Free' hormone (i.e., unbound to antiserum) remains on the column after a second wash. The radioactivity on the column is counted and related to the total activity added. The T3 standards produced a straight line on log logit plot; reactivity of analytical grade thyroxine was 0.6% on weight basis; and the analytical recovery of T3 added to a T3 free serum was complete. Euthyroid, hyperthyroid, and hypothyroid ranges were 0.74-2.64, 2.91-7.52, and 0-1.21 μg/liter, respectively. These values correlated well with both the clinical status of patients and with values obtained by an established radioimmunoassay method. The procedure is simply done; results may be obtained in less than 4 h.