Radioimmunoassay of Thyroxine in Unextracted Serum, by a Single-Antibody Technique

Abstract

Abstract A radioimmunoassay procedure for thyroxine (T4) is described, for which only 25 µl of serum is required. The antibody, commercially available, is produced in rabbits in response to injections of a T4—albumin conjugate. Native T4—binding proteins are denatured by heating 25 µl of serum in 0.2 ml of a glutamate buffer in a boiling water bath. After a 1-h incubation of heat-treated serum with I125-T4 and T4 antibody, "free" and "bound" T4 are separated by use of hemoglobin-coated charcoal. The method has excellent sensitivity, is rapid, and possesses significant advantages over a standard competitive protein binding method with which it is compared.