Comparison of specific immunoassays for detection of the β-core human chorionic gonadotrophin fragment in body fluids

Abstract

ABSTRACT We have validated two new methods, one radioimmunoassay (RIA) and one immunoradiometric assay (IRMA), for the detection of β-core hCG fragment (βC-hCG) in body fluids. In addition, we have compared their performance with two other assays designed for βC-hCG quantification. The RIA uses a rabbit polyclonal antibody raised against pure βC-hCG which has a high affinity constant, is sensitive to 5 pmol/l, and has significant cross-reaction only with the free βLH subunit. The IRMA, designed in a liquid phase, uses the same polyclonal antibody associated with a 125I-labelled mouse monoclonal antibody (32H2) raised against βhCG, 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 βC-hCG in urine from healthy pregnant women (n = 47) and gave correlation coefficients higher than r= 0·960 with any combination. Analysis of βC-hCG in urine of non-pregnant subjects (n= 238) showed measurable βC-hCG in 8·8% (levels ranged from 5 to 34 pmol/l) with the IRMA and 88·3% with the RIA (n=30; ranging from 28·4 to 228 pmol/l) (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 βC-hCG in pregnancy urine. However, the IRMA appears to be more appropriate for βC-hCG analysis in non-pregnant individuals, specifically in postmenopausal women because of the high cross-reactivity of the RIA with free βLH or β fragments of other glycoproteins. These studies have significance for our understanding of the physiology of βC-hCG in cancer, pregnancy and after the menopause, Journal of Endocrinology (1992) 135, 161–174