A Simple, But Reliable Assay of Sex Hormone Binding Globulin

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Abstract
The likelihood of erroneous results is very high when a single dose of ligand (e.g. dihydrotestosterone) is employed in the assay of sex hormone binding globulin (SHBG) using precipitation with ammonium sulfate. However, correct results will be obtained if several ligand doses are used and the calculations are based on a Scatchard plot from which non-specific binding has been eliminated. The reliability of such a multiple-dose SHBG assay was tested. As established by an analysis of variance, the results of the measurements were independent of the volume assayed. Furthermore, by assaying 25 plasma sample in duplicate, an average within-assay coefficient of variation of 5.5% was obtained. The assay of the same samples on different occasions gave an estimate of between-assay variation ranging from 3.5% to 8.9% for various types of plasma. Moreover, the results of the assay of 170 plasma samples were well correlated (r = 0.8) with those obtained by a steady state electrophoresis. Thus the multiple-dose precipitation assay gives reliable results and is suitable for routine measurements of SHBG.