Use of an immunoradiometric assay and a radioimmunoassay for the detection of free beta-human chorionic gonadotropin.

An immunoradiometric assay and a radioimmunoassay (RIA) were used to quantitate human chorionic gonadotropin (hCG) in the sera of ten pregnant women at term and of six women with gestational trophoblastic neoplasia. The two techniques show good correlation (Pearson correlation coefficient .96) in the assay of pregnancy serum. Because only the RIA, and not the immunoradiometric assay, measures the free beta-subunit of hCG, a comparison of the results obtained by the two immunoassay methods permits a semi-quantitative assessment of the free beta-subunit. The numerical results may not reflect the actual concentration of free beta-subunit in that two different immunoassay methods are used.