Simplified method for measuring sex-hormone binding globulin.

We describe a simple, rapid method for measurement of sex-hormone binding globulin. Serial dilutions of pregnancy serum are prepared in serum from males that has been pre-treated by heating to 60 degrees C for 1 h to destroy endogenous binding globulin, which is then determined by a long-used technique to yield a set of "standards." In the assay itself, a fixed amount of [3H]-labeled and unlabeled dihydrotestosterone is incubated with standard or unknown, and the bound fraction precipitated with saturated ammonium sulfate. A plot of percent of the steroid bound vs standard dilution yields a sigmoid curve, from which the results in unknowns can be read by simple extrapolation. Within-assay CVs for pools of serum from men, women, and women in late pregnancy were 6.56, 9.59, and 8.4%, respectively. Between-assay CVs for the same pools were 8.05, 9.5, and 11.5%, respectively. The correlation between results obtained by this method and those of the older technique was 0.95 for samples from non-pregnant subjects and 0.73 for those from pregnant women. Our procedure is simpler and faster than previous methods and accurately measures the differences in the globulin in sera from men, women, and pregnant women. Forty to 50 samples can be assayed in a working day.