Sandwich-type enzyme immunoassay for human chorionic gonadotropin

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Abstract
We have developed a sandwich-type enzyme immunoassay for human chorionic gonadotropin (hCG), in which antibody Fab’-β-D-galactosidase complex and an antibody-immobilized silicone rubber solid phase were used. Despite the fact that this assay system cross-reacted about 40% with human luteinizing hormone (LH) that contains an immunologically very similar subunit to that of hCG, it proved to be highly sensitive with hCG measurable at levels as low as 0.3 mlU per assay tube. Using 25 μl of serum sample or 100 μl of urine sample, hCG levels in serum (10–1000 mlU/ml) or in urine (3–300 mlU/ml) could be determined with the same degree of precision as in radioimmunoassay without sample interference with the assay. The coefficients of variation in within-run, and between-run were 9.2–13.3%, and 4.2–18.8%, respectively. Values obtained with enzyme immunoassay correlate well with those of radioimmunoassay (r = 0.961, slope = 1.129, y-intercept = 3.7 mlU/ml for 35 serum samples) and hemagglutination assay (r = 0.954, slope = 0.951, y-intercept = 1.8 mlU/ml for 88 urine samples).