Ultrasensitive immunoradiometric assay for chorionic gonadotropin which does not cross-react with luteinizing hormone nor free beta chain of hCG and which detects hCG in blood of non-pregnant humans.

We have developed a sensitive, non-competitive, two-monoclonal antibody, sandwich-type or immunoradiometric assay for human chorionic gonadotropin (hCG) which shows no cross-reaction with the free beta chain of hCG nor with human luteinizing hormone (LH). In the assay procedure, two, highly selected monoclonal antibodies reacted in solution with hCG to be quantified. One antibody was covalently conjugated to biotin. This antibody was specific for the beta subunit of hCG, and showed no reaction with LH nor the alpha subunit. The second antibody was labelled with 125I and was specific for intact hCG and LH, showing no cross-reaction with beta hCG nor the alpha subunit. The separation system was a polystyrene ball conjugated with biotin. This ball bound via an avidin bridge the monoclonal 'sandwich' containing hCG. Counts per minute bound to the ball were directly proportional to the amount of hCG present. The assay was specific for whole hCG and showed no reaction with beta hCG, beta LH, intact LH nor the free alpha subunit. Sensitivity was adequate to detect 'hCG-like' material in all post menopausal women and, when single samples were obtained, in over 2/3 of normal men. When multiple samples were obtained, 'hCG-like' material was detectable in all eugonadal adults studied.