Analytical problems associated with HCG assayBMJ 2008; 337 doi: https://doi.org/10.1136/bmj.a2076 (Published 13 October 2008) Cite this as: BMJ 2008;337:a2076
- Julian H Barth, consultant chemical pathologist1
Sebire and Seckl state that gestational trophoblastic disease is monitored by measuring serum human chorionic gonadotrophin (HCG), but they do not discuss the analytical problems associated with this assay.1
Numerous reports of interference with this assay have been made since 1984, the most important by Rotmensch and Cole in 2000.2 They reported on 12 women who had a false diagnosis, 11 of whom had been subjected to needless, and in some cases quite extensive, surgery or chemotherapy. The problem has not disappeared and we still uncover cases of assay interference in women who have serial HCG measurements for pregnancy testing. The frequency of HCG interference is unknown, but in our study of thyroid and gonadotrophin assays we detected clinically relevant interference in 0.5% of all assays.3
A further problem is in the variation between assays provided by different manufacturers. Mitchell and Seckl clearly showed this variation in a patient with tumours whose HCG was detectable in some assays but undetectable in others.4
HCG assays are approved by the regulatory authorities for pregnancy testing alone, and the risk to patients with trophoblastic disease or germ cell tumours will continue until assays are formally validated for these diseases.
Cite this as: BMJ 2008;337:a2076
Competing interests: None declared.