Analytical and clinical evaluation of a human chorionic gonadotrophin plus β (hCG + βhCG) immunoassay in germ cell tumours and gestational trophoblastic disease

Abstract Background. – In gestational trophoblastic disease (GTD) and germ cell tumours (GCT), irregular human chorionic gonadotrophin (hCG) forms may be the principal source of immunoreactivity. These hCG variants are detected in a variable manner by commercial hCG immunoassays. Methods. – We analytically evaluated the automated electrochemiluminescent Elecsys hCG+β assay (second version) from Roche Diagnostics and compared the method with a free β-hCG IRMA in 248 follow-up samples from 15 patients with GTD or GCT. Results. – Intraassay and interassay imprecision were, respectively ≤ 2% and 5%. Functional sensitivity was ≤ 0.25 IU/l. We found 19 discordant results in 248 samples (7.7%) measured with both the hCG+β and the free β-hCG assay. All 19 were ≤ to the detection limit of the free β-hCG assay and > to the normal cut-off value in the hCG+β assay. An increased half-life of hCG (resulting in delayed clearance) in comparison to free β-hCG can explain 13 of the 19 discordant results. The remaining discordant samples suggest an increased sensitivity of the Elecsys hCG+β assay in comparison to the free β-hCG IRMA, probably because of the broad reactivity of the former for clinically relevant hCG isoforms (intact, nicked, β-core and free β-hCG). Conclusion. – The Elecsys hCG+β assay is a sensitive and precise automated method and is reliable for monitoring patients with GTD and GCT.