COMPARISON OF SPECIFIC IMMUNOASSAYS FOR DETECTION OF THE BETA-CORE HUMAN CHORIONIC-GONADOTROPIN FRAGMENT IN BODY-FLUIDS

We have validated two new methods, one radioimmunoassay (RIA) and one immunoradiometric assay (IRMA), for the detection of beta-core hCG fragment (betaC-hCG) in body fluids. In addition, we have compared their performance with two other assays designed for betaC-hCG quantification. The RIA uses a rabbit polyclonal antibody raised against pure betaC-hCG which has a high affinity constant, is sensitive to 5 pmol/l, and has significant cross-reaction only with the free betaLH subunit. The IRMA, designed in a liquid phase, uses the same polyclonal antibody associated with a I-125-labelled mouse monoclonal antibody (32H2) raised against betahCG, is sensitive to 1.5 pmol/l, and does not cross-react significantly with any related glycoprotein. Comparison between these two assays and two others previously published was made by measuring betaC-hCG in urine from healthy pregnant women (n = 47) and gave correlation coefficients higher than r = 0.960 with any combination. Analysis of betaC-hCG in urine of non-pregnant subjects (n = 238) showed measurable betaC-hCG in 8.8% (levels ranged from 5 to 34 pmol/1) with the IRMA and 88.3% with the RIA (n = 30; ranging from 28.4 to 228 pmol/1) (P = 0.05). We concluded that, despite different affinities of the antibody involved and different cross-reactivities with related glycoproteins, the four assays we examined may be equally employed to detect betaC-hCG in pregnancy urine. However, the IRMA appears to be more appropriate for betaC-hCG analysis in non-pregnant individuals, specifically in postmenopausal women because of the high cross-reactivity of the RIA with free betaLH or beta fragments of other glycoproteins. These studies have significance for our understanding of the physiology of betaC-hCG in cancer, pregnancy and after the menopause,