Development and validation of a choriogonadotropin beta-subunit radioimmunoassay for serum choriogonadotropin using...

A sensitive, specific, accurate and precise radioimmunoassay procedure developed for the beta-subunit of serum choriogonadotropin (hCGbeta) is described. 1. The assay employs an anti-hCGbeta (rabbit) serum generated against hCGbeta, highly purified intact choriogonadotropin (hCG) as standard, and [125I]hCG as the radioactive ligand. The antibody-bound hCG was separated from the free hormone by the addition of goat anti-rabbit gamma-globulin. 2. The detection limit of the assay was approximately 75 microIU hCG which corresponds to a serum concentration of approximately 0.75 mIU/mL. 3. Cross reactivity studies performed with human luteinizing hormone (hLH) and human thyroid-stimulating hormone (hTSH) indicated minimal interferences from these structurally similar glycoproteins. Parallel dose-response curves were demonstrated between dilutions of sera with elevated hCG concentrations and the standard reference preparation. A non-specific binding of less than 2.5% of the total [125I]hCG was routinely observed. 4. The analytical recovery of hCG added to human sera varied from 94 to 110%, with a mean recovery of 101%. 5. The inter-assay variation was determined by assaying (n=30) 3 different quality control pools. The following data were obtained: X1=4.6 +/- 0.5 mIU/mL (CV=10.9%); X2=8.1 +/- 0.9 mIU/mL (CV=11.1%); and X3=36.8 +/- 2.8 mIU/mL (CV=7.6%). 6. The clinical data collected from subjects with trophoblastic disease agreed with previously published studies. All of the reagents are available commercially.