Choriogonadotropin measured with the Tandem-E immunoenzymetric assay system

We evaluated the Hybritech Tandem-E procedure for quantifying choriogonadotropin (hCG) in human serum. In this "sandwich"-type assay, two monoclonal antibodies directed against different regions of the hCG molecule are used, one coated on a plastic bead, the second conjugated to alkaline phosphatase. The assay can detect as little as 1.0 int. unit of the hormone per liter, shows a linear response up to at least 200 int. units/L, and has good precision. By prolonging the incubations for formation of the sandwich and for substrate hydrolysis, one can achieve higher sensitivity at the expense of a narrower linear range. Correlation with a conventional radioimmunoassay for the beta subunit of hCG was generally excellent, but in one instance the Tandem-E gave an apparently false positive result.