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

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%). Betweenmethod 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.