Radioimmunoassay of free beta-subunit of human chorionic gonadotropin as a prognostic test for persistent trophoblastic disease in molar pregnancy.

A new radioimmunoassay system was established with a monoclonal antibody (1E5) that distinguishes the free beta-subunit of human chorionic gonadotropin in the presence of intact human chorionic gonadotropin, showing only 0.23% cross-reactivity with the intact human chorionic gonadotropin molecule and virtually no cross-reactivity with other glycoprotein hormones or their beta-subunits. Serum samples, taken at initial diagnosis from nine patients with hydatidiform mole and spontaneous remission and 12 patients with subsequent progression to persistent trophoblastic disease, were assayed for free and total levels of the beta-subunit of human chorionic gonadotropin. The assay results were expressed as a ratio of nanograms of free beta-subunit per 1000 mIU of total beta-subunit. Eight of nine patients with mole and spontaneous remission had a ratio value less than 4 whereas 10 of 12 patients with subsequent persistent disease had a ratio value greater than 4. Statistical analysis with chi 2 showed a highly significant correlation of high ratios with eventual progressive disease (p = 0.0009). This study suggests that excessive production of the free beta-subunit of human chorionic gonadotropin may identify patients with a high likelihood of developing persistent trophoblastic disease.