Radioimmunoassay of free β-subunit of human chorionic gonadotropin in diagnosis of high-risk and low-risk gestational trophoblastic disease

A radioimmunoassay was performed with monoclonal antibody 1E5, which distinguishes free β-subunit of human chorionic gonadotropin in the presence of intact human chorionic gonadotropin. Serum samples were obtained from 68 pregnant women, 9 with hydatidiform mole who underwent spontaneous remission, 12 with hydatidiform mole who developed gestational trophoblastic disease, 5 with metastatic gestational trophoblastic disease of high-risk category, and 1 with choriocarcinoma concomitant with pregnancy. The concentrations of free β-subunit of human chorionic gonadotropin and total β-subunit were determined on the sera. The assay data were expressed as a ratio of nanograms of free β-subunit per 1000 mIU of total β-subunit. The ratios, analyzed by the Wilcoxon two-sample test, indicated a highly significant correlation between high ratios and the eventual diagnosis of high-risk gestational trophoblastic disease (p = 0.0019). This study suggests that the excessive production of free β-subunit of human chorionic gonadotropin may identify patients with high-risk gestational trophoblastic disease much earlier and identify gestational trophoblastic disease in patients during pregnancy.