Free testosterone concentration in serum: a method for determination.

Two procedures for quantifying serum levels of testosterone-estradiol-binding globulin (TeBG) have been evaluated. Both procedures utilize indirect methods for assessing the extent of protein-steroid interaction for the purpose of devising a clinically feasible procedure for estimating serum free testosterone. In the first method serum protein concentration was varied by dilution until 50 per cent of steroid binding was obtained at a given concentration of steroid. Dextran-coated charcoal was used for separating TeBG-bound steroid from the unbound fraction. In the second procedure DEAE-cellulose filtration was used to isolate the TeBG-steroid complex for quantitation. Having a sufficiently accurate measure of TeBG levels together with a knowledge of the total endogenous testosterone permitted the estimation of serum free testosterone based on the binding affinities of serum proteins. The preferred DEAE-cellulose filtration method has proved useful for routine clinical evaluation of physiologically effective androgen levels.