Received on January 29, 2009
Accepted on April 24, 2009

Cancer Diagnostics

Differences in Recognition of the First WHO International Reference Reagents for hCG-Related Isoforms by Diagnostic Immunoassays for Human Chorionic Gonadotropin

¹ Department of Clinical Biochemistry, Royal Infirmary, Edinburgh, UK
² Institute for Biomedical Aging Research, Austrian Academy of Sciences, Innsbruck, Austria
³ Department of Clinical Biology, Institut Gustave-Roussy, Villejuif, France
⁴ Department of Obstetrics and Gynecology, College of Physicians and Surgeons of Columbia University, NY, NY
⁵ National Institute of Biological Standards and Control, Potters Bar, UK
⁶ Research Centre for Reproductive Health, Department of Obstetrics and Gynaecology, University of Adelaide, The Queen Elizabeth Hospital, Woodville, Australia
⁷ Department of Clinical Chemistry, Helsinki University Central Hospital, Finland
⁸ Department of Clinical Biochemistry, Royal Infirmary, Edinburgh, UK; Institute for Biomedical Aging Research, Austrian Academy of Sciences, Innsbruck, Austria; Department of Clinical Biology, Institut Gustave-Roussy, Villejuif, France; Department of Obstetrics and Gynecology, College of Physicians and Surgeons of Columbia University, NY, NY; National Institute of Biological Standards and Control, Potters Bar, UK; Research Centre for Reproductive Health, Department of Obstetrics and Gynaecology, University of Adelaide, The Queen Elizabeth Hospital, Woodville, Australia, and Department of Clinical Chemistry, Helsinki University Central Hospital, Finland

^* To whom correspondence should be addressed. E-mail: C.Sturgeon{at}ed.ac.uk.

BACKGROUND: The first WHO International Reference Reagents (IRRs) for 6 human chorionic gonadotropin (hCG)-related molecular variants, highly purified and calibrated in substance concentrations by the IFCC Working Group for hCG, permit experimental elucidation of what commercially available hCG methods measure in molar terms and enable assessment of their fitness for clinical purposes.

METHODS: Pools containing known amounts of the IRRs spiked into normal human serum were issued to participants through the UK National External Quality Assessment Service for hCG for a period of 7 years. Among 16 assays used, 4 recognized only hCG, whereas 6 recognized hCG and its free -subunit (hCG), and 6 recognized hCG, hCG, and the hCG core fragment.

RESULTS: Differences in calibration of current hCG assays are moderate. Mean recovery of the current International Standard (IS), hCG IS 75/589, was 107% (range 93% to 126%), whereas that of the IRR 99/688 for hCG was 139% (range 109%–164%). Between-method variation for the latter (CV 12.3%) was also greater than for IS 75/589 (CV 8.8%). Recognition of hCG varied markedly (CV 37%). Most assays led to overestimation, but 2 RIAs produced results that were slight underestimations. Recognition of the hCG core fragment was even more variable (CV 57%) and was closest to equimolarity for the RIAs.

CONCLUSIONS: Assays for hCG show considerable variation in their recognition of various forms of hCG, and this variablility is the most important cause of method-related differences in hCG results in serum and an even more important cause of method-related differences in urine measurements. Equimolar recognition of the major hCG isoforms is essential if between-method comparability for hCG is to be improved.