Positive interference by danazol in a testosterone radioimmunoassay kit procedure

We describe a problem in measuring serum testosterone concentrations in the serum of women who are taking danazol. The Diagnostic Products Corporation testosterone radioimmunoassay gives very high apparent testosterone concentrations in these women and the value obtained depends on the volume of serum extracted per assay tube. Chromatography of the serum extracts on Sephadex LH-20, but not on Celite, before radioimmunoassay reduced these high apparent testosterone concentrations to less than that found in normal women.