Specific enzyme immunoassay for human chorionic gonadotrophin.

A sandwich-type enzyme immunoassay system specific for human chorionic gonadotrophin (hCG) was prepared with the antibody Fab'-beta-D-galactosidase complex and the antibody F(ab')2-immobilized silicone rubber solid phase by using a purified antibody to beta subunit of hCG (hCG beta). The assay system cross-reacted less than 4% with human luteinizing hormone (hLH) and human follicular stimulating hormone (hFSH), and proved to be highly sensitive with hCG measurable at levels as low as 0.3 mIU per assay tube. Using 50 microliter of serum sample, 6-600 mIU/ml of hCG in serum could be determined specifically with the same degree of precision as in radioimmunoassay but without sample interference with the assay. The coefficients of variation within-run and between-run were 8.6-8.9%, and 4.9-10.7%, respectively. Values obtained with the enzyme immunoassay correlated well with those of radioimmunoassay (r = 0.98, slope = 0.94, y-intercept = 10.2 mIU/ml for 75 serum samples). Results of the immunoassay of hCG levels in serial samples of serum from healthy women and patients with choriocarcinoma show that this method is useful in the clinical diagnosis of trophoblastic disease.