Radioimmunoassay of Thyrotropin Concentrated from Serum

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Abstract
A method for concentrating human TSH [thyrotropin] (hTSH) from serum for use in RIA [radioimmunoassay] is described. The method takes advantage of the affinity of the plant lectin, concanavalin [Con] A, for the carbohydrate portion of the hTSH molecule. The hTSH from 2.5 ml serum was adsorbed to ConA covalently linked to sepharose and then radioimmunoassayed using the hTSH antiserum and hTSH for iodination distributed by the National Pituitary Agency. For the RIA standard curve, the hTSH reference preparation was concentrated from a serum with undetectable hTSH in order to correct for recovery and to control for nonspecific effects. The percentage of serum hTSH extracted from 2.5 ml serum with the concentration procedure was 76.6 .+-. 3.4% (mean .+-. SD). The coefficient of correlation between serum hTSH, determined with the concentration procedure, and serum hTSH determined without was 0.979 (P < 0.001). Over 95% of normal adult men and women had detectable levels of serum hTSH, ranging from < 0.56-4.0 .mu.U[microunits]/ml. The mean of detectable serum hTSH levels in normal adult women (n = 11) was 1.54 .+-. 1.03 .mu.U/ml (mean .+-. SD) and in normal men (n = 9) was 2.02 .+-. 1.15 .mu.U/ml (mean .+-. SD). Clinically hyperthyroid patients with diffuse and nodular toxic goiters (n = 8) and patients with hypothyroidism secondary to pituitary disease (n = 6), 4 of whom were taking replacement doses of thyroid hormone, had undetectable serum hTSH levels. Serum hTSH in patients with primary hypothyroidism uniformly exceeded the normal range. This hTSH concentrating procedure enhances the effective sensitivity and the clinical utility of the RIA for hTSH in serum.

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