Comparison of human chorionic gonadotrophin concentrations in the sera of patients with normal and abnormal pregnancy measured by radio-immunoassay and immunoradiometric assay.

Human chorionic gonadotrophin (HCG) concentrations were measured in the serum of 40 patients with normal pregnancy, 18 with ectopic pregnancy, 36 with incomplete abortions and 24 patients with gestational trophoblastic disease using a radio-immunoassay (RIA) and immunoradiometric assay (IRMA). There were no significant differences in HCG concentrations measured by the two assays with regard to the first three groups but the patients with gestational trophoblastic disease had consistently higher results on RIA, probably reflecting increased circulating free beta-subunit of HCG. It was concluded that measurement of HCG using IRMA for the intact molecule gives equivalent results to RIA in patients with normal and ectopic pregnancy as well as after abortion. However, monitoring of patients with choriocarcinoma and hydatidiform mole requires an assay that detects free beta-HCG.