Experience of discordant βhCG results by different assays in the management of non-seminomatous germ cell tumours of the testis

Fifty-five patients with non-seminomatous germ cell tumours (NSGCT) who were referred to a regional clinical oncology centre over a 3-year period were assessed prospectively with assays of the serum tumour markers alpha-fete protein (AFP) and beta-human chorionic gonadotropin (beta hCG). Paired baseline beta hCG assays were undertaken using a polyclonal radioimmunoassay (RIA) and a monoclonal fluoroimmuno assay (FIA). Serial paired measurements were undertaken in patients showing discordance on baseline assays, Four patients (7%; 95% confidence interval 0-14) showed discordance between the paired beta hCG assays. Of these, two showed elevated beta hCG on RIA, with normal levels on FIA; two showed elevated beta hCG on FIA, with normal levels on RIA. No discordance was noted with AFP assays. Discordance persisted in two of the patients (50%) and disappeared on treatment in one (25%); one patient died during treatment. Discordant beta hCG assays present difficulties in interpretation and have therapeutic implications in patients with NSGCT. No single currently available assay is conclusive in all. patients and commercial assay kits should be chosen with care.