Interference of Luteinizing Hormone [Beta]-Core Fragment in Urinary Gonadotropin Assays (Letters) (Letter to the Editor‪)‬

To the Editor: Iles et al. (1) speculated on the value of development of a specific assay to measure human luteinizing hormone [beta]-core fragment (hLH[beta]cf) without cross-reactivity with human chorionic gonadotropin [beta]-core fragment (hCG[beta]cf). We wish to draw readers' attention to the fact that we developed and reported such a specific assay for hLH[beta]cf in 1995 (2) and reviewed the applications of this assay in 1996 (3). We wrote (3) that the assay "may have useful applications in tumor marker assays, pregnancy tests, and menopause". The hLH[beta]cf assay (B505-B503*) exhibits 1% cross-reactivity with hLH and 0.1% cross-reactivity with hCG[beta]cf. We found that the assay detects the urinary form of hLH[beta]cf in the urine of normally ovulating women (2). We applied this assay to the urine of postmenopausal women and found significant quantities of hLH[beta]cf but not hCG[beta]cf. The mean concentration of hLH[beta]cf for 107 samples from postmenopausal women was 236 pmol/g creatinine (4). We also measured hCG[beta]cf in the same samples and found that its concentration was one-tenth that of hLH[beta]cf. For hCG[beta]cf, we used our laboratory assay B210B108* (5), which has 2% cross-reactivity with hLH[beta]cf. These data suggest that to use hCG[beta]cf as a cancer marker, an assay of very high specificity for this molecule is required because of possible cross-reaction with hLH[beta]cf.