Convenient radioimmunoassay for urinary human choriogonadotropin without interference by urinary human lutropin

We have devised a radioimmunoassay (RIA) for human choriogonadotropin (hCG) in first morning-voided urine specimens. Concanavalin A, a lectin, is used to extract and concentrate the hCG from urine. A high-affinity antiserum is used, directed to the hCG beta carboxy-terminal peptide, a unique immunological determinant not shared by the beta subunit of human lutropin. This ensures that urinary human lutropin-related molecules, which interfere with RIAs involving antisera to the intact hCG beta subunit, will not cross react in this assay. A concentrations of hCG as low as 0.4 microgram/L can be detected in the first morning-voided urine. The effective sensitivity of this assay for the unequivocal detection of hCG production is somewhat better than that achieved with the serum hCG RIA involving antisera to the hCG beta subunit. The improved specificity and sensitivity of this assay, and the greater convenience of collecting samples of urine rather than blood, are clinical useful advantages of this approach to assessing hCG production in humans.