Cross-reaction with luteinizing hormone beta-core is responsible for the age-dependent increase of immunoreactive beta-core fragment of human chorionic gonadotropin in women with nonmalignant conditions.
Iles RK., Javid MK., Gunn LK., Chard T.
BACKGROUND: The beta-core fragment of human chorionic gonadotropin (hCGbetacf), also termed "beta-core" and urinary gonadotropin peptide (UGP), has been reported to be present in the urine of healthy women and to increase in concentration after menopause. This could reflect cross-reaction with the equivalent metabolite of luteinizing hormone (LH), the beta-LH-core. METHODS: We measured immunoreactive LH, hCG, free alpha-subunit, and free beta-subunit hCG (hCGbeta), as well as beta-core, using the S504 RIA and Triton UGP enzyme immunoassay in 274 urine samples from women with nonmalignant gynecological conditions. The molar cross-reaction of each assay with purified beta-LH-core was determined. RESULTS: Cross-reaction with beta-LH-core was 100% in the LH and the S504 beta-core assay, 5% in the Triton UGP assay, and <0.1% in the hCG, free alpha-subunit, and free hCGbeta assays. Median urine concentrations of all analytes showed an age-dependent increase. LH and free alpha-subunit concentrations were approximately 10(3) pmol/mol creatinine; hCG and S504 beta-core were approximately 10(2) pmol/mol creatinine; free hCGbeta and Triton UGP beta-core were in the tens of pmol/mol creatinine. The S504 beta-core concentrations were 10% of those of LH. S504 beta-core was strongly correlated with LH, but not with hCG or with free hCGbeta (LH, r2 = 0.45; hCG, r2 = 0.26; free hCGbeta, r2 = 0.03). The concentrations of beta-core detected by the Triton UGP assay, which has a 5% cross-reaction with beta-LH-core, were 2% of LH and 5% of the S504 beta-core concentrations. Triton UGP values correlated strongly with LH concentrations, but less well with S504 beta-core, intact hCG, and free hCGbeta (LH, r2 = 0.44; S504 beta-core, r2 = 0.33; hCG, r2 = 0.32; free hCGbeta, r2 = 0.19). CONCLUSIONS: Immunoreactive beta-core in women free of malignancies reflects cross-reaction with concentrations of the metabolite of LH, beta-LH-core, within the health-related reference interval.