A specific and sensitive radioimmunoassay for human choriogonadotropin

A specific and sensitive radioimmunoassay for human choriogonadotropin (hCG) has been developed using rabbit antiserum to chemical analogs of beta subunit of human chorionic gonadotropin prepared by controlled reduction and S-alkylation of its disulfide linkages. The assay was highly specific for hCG as the binding of [125I]-hCG to the antibody was not affected by standard human lutropin, by human male serum, postpartum serum from women, serum from post-menopausal women and human menopausal gonadotropin (Pergonal). The assay was highly sensitive, the minimal detection limit in terms of highly purified hCG (L-129, 12500 IU/mg) being 1 ng/ml or 0.2 ng/tube (or 12 mlU/ml in terms of WHO 2nd international reference preparation of hCG). Using this assay we were unable to detect any immunoreactive hCG in human tissues like lung, liver and colon. The high specificity, sensitivity, accuracy and reproducibility of the assay make this a highly desirable radioimmunoassay for human choriogonadotropin.