Cross-reactivity of a commercial chemiluminescence immunoassay for human chorionic gonadotropin with the free beta-subunit.

An enhanced chemiluminescence immunoassay for the determination of serum human chorionic gonadotropin (HCG) in specimens from oncology patients has been assessed with respect to its cross-reactivity with the free HCG beta-subunit (HCG-beta). The assay, standardized against the First International Reference Preparation 75/537, had a cross-reactivity with the free beta-subunit of 625% (molar basis). Therefore this assay achieves high sensitivity for the detection of either intact HCG or free HCG-beta in serum of patients with seminomatous or nonseminomatous testicular cancers. Results of both assays, the in-house immunoradiometric assay (+HCG-beta) and the Amerlite HCG-60 assay, showed a close correlation (R = 0.854-0.960) when serum samples from tumour patients were analyzed. Moreover, the content of free beta-subunit determined in a specific HCG-beta assay, could be quantitatively measured in the enhanced chemiluminescence immunoassay. Thus, this assay is suitable for oncology use, but also highlights the limitations of measuring HCG in serum samples.