Solid-phase chemiluminescence immunoassay for progesterone in unextracted serum.

We describe a simple, solid-phase chemiluminescence immunoassay for progesterone in 10 microL of unextracted serum ("direct" assay). Danazol at pH 8.0 is included (100 ng per tube) to displace progesterone from binding proteins in serum. A progesterone-11 alpha-hemisuccinyl-aminobutylethyl isoluminol conjugate serves as the chemiluminescent ligand marker and homologous antiprogesterone IgG covalently coupled to "Immunobeads" is the immunoadsorbant. After the binding reaction, bound and free ligand are separated by centrifugation and the chemiluminescence yield of the bound label is determined. The sensitivity, specificity, precision, and accuracy of the method are similar to those of a conventional radioimmunoassay for progesterone in which a radioligand of tritiated progesterone and serum extraction are used. Progesterone values obtained by this procedure agreed well (r = 0.987) with those obtained by radioimmunoassay. We conclude that the chemiluminescence immunoassay for progesterone in unextracted serum is analytically valid and offers a convenient alternative to radioimmunoassay.