Radioimmunoassay of plasma testosterone, with use of polyethylene glycol to separate antibody-bound and free hormone.

We have developed a reliable radioimmunoassay for testosterone in plasma, polyethylene glycol ("Carbowax 6000") being used to separate antibody-bound and free hormone. Testosteron is separated from interfering steroids, notably dihydrotestosterone, by liquid-liquid partition chromatography on infusorial earth (Celite). The assay is sensitive (9 pg for standards), precise, and accurate. The lowest measurable concentration fo testosterone is 350 ng/liter for plasma from men and 70 ng/liter for plasma from women. Intra- and inter-assay coefficients of variation were 6.9% and 9.7%, respectively, for plasma from men, and 9.6% and 11.8%, respectively, for plasma from women. Our method for separating antibody-bound and free hormone is practical and convenient and may be generally applicable to all radioimmunoassays of steroid hormones in plasma.