Evaluation of nicked human chorionic gonadotropin content in clinical specimens by a specific immunometric assay

We report the development and characterization of an IRMA for the direct me asurement of nicked human chorionic gonadotropin (hCGn) in blood and urine. hCGn derived from a reference preparation of hCG used as an immunogen elic its monoclonal antibodies (mAbs) with enhanced recognition of human luteini zing hormone epitopes. The most specific assay for pregnancy hCGn is an IRM A composed of one mAb to choriocarcinoma-derived hCGn (C5) and a second mAb developed from immunization with normal-pregnancy hCGn. This assay was use d to evaluate hCGn profiles in normal, in vitro fertilization, Down syndrom e, and ectopic pregnancies. In all pregnancies, hCGn was usually present in much lower concentrations than the non-nicked hCG isoform. Our results sug gest that some form of physical separation from the overwhelming quantities of non-nicked hCG present in clinical specimens will be required before ac curate immunochemical estimations of hCGn can be made.