Interference of danazol with the radioimmunoassay of steroid hormones

The crossreactivity of Danazol, a synthetic steroidal drug with antigonadotropic and impeded androgenic properties, with 12 different antisera against 8 different steroids was studied either by conventional competitive inhibition assay or by competitive saturation assay, the latter of which was found to be more sensitive. It was shown that Danazol strongly reacted with an antiserum against 5 alpha-dihydrotestosterone and also, albeit to a much lesser extent, with antisera against testosterone, cortisol and progesterone in decreasing order. It did not interfere with RIA-systems for 11-desoxycortisol, 17 alpha-hydroxyprogesterone, estradiol-17 beta and estriol. However, out of four antisera against estradiol-17 beta two were found to considerably crossreact with Danazol which might explain apparent increases in plasma levels of this hormone during Danazol treatment as recently reported.