A Simple Robust Assay for Testosterone in Male Plasma Using an 125 I-Radioligand and a Solid-Phase Separation Technique

Abstract

A radioimmunoassay for testosterone in male plasma utilising a gamma-emitting radioligand and a solid-phase antiserum is described. The radioligand is testosterone-3-(O-carboxymethyl)-oxime coupled to ¹²⁵I-iodohistamine, and the solid-phase antiserum is prepared by coupling antitestosterone-3-bovine serum albumin to cyanogen bromide activated cellulose. The new procedure retains much of the specificity associated with a published, specific radioimmunoassay using an antiserum raised against testosterone-11α-BSA and a tritium radioligand and incorporating a dextran-coated charcoal separation procedure; values obtained by the two procedures are in excellent agreement (r = 0·98, n = 20).

The combination of an ¹²⁵I-radioligand and a solid-phase separation technique greatly increases sample throughput and has the further advantage of reduced running costs and a greater potential for automation. The method gives satisfactory levels of sensitivity, precision, and accuracy.