SIMULTANEOUS DETERMINATION OF FREE TESTOSTERONE AND TESTOSTERONE BOUND TO NON-SEX-HORMONE-BINDING GLOBULIN BY EQUILIBRIUM DIALYSIS

We describe a procedure based on equilibrium dialysis that allows the simultaneous determination of free testosterone and testosterone bound to non-sex-hormone-binding globulin (non-SHBG) in plasma. After satur ating SHBG with 5alpha-dihydrotestosterone (DHT) according to a techni que recently described, the percentage of free testosterone in the tre ated and the untreated samples is measured by equilibrium dialysis wit h use of a semiautomated instrument that allows rigorous standardizati on of the experimental conditions. The present method is simpler and f aster than the previously described technique in which, after the satu ration of SHBG with DHT, the unbound fractions were measured by centri fugal ultrafiltration dialysis. The method is also reproducible and su ited for the analysis of a large number of samples. The technique has been applied to the determination of the fractional distribution of te stosterone in plasma pools from normally menstruating, pregnant, and p ostmenopausal women and from normal men.