Detection of early pregnancy forms of human chorionic gonadotropin by home pregnancy test devices

Abstract

Background: Home pregnancy testing devices claim >99% diagnostic accuracy for pregnancy and utility on the first day of the missed menses or earlier. We investigated the forms of human chorionic gonadotropin (hCG) in early pregnancy urines, the diagnostic accuracy claim, and the abilities of 15 devices to detect the different forms of hCG. Methods: We measured the concentrations of regular hCG and hyperglycosylated hCG (H-hCG, a large hCG variant) in 592 urines. Fifteen home devices were tested according to manufacturers' instructions with regular hCG and H-hCG diluted in urine. Results: H-hCG was the principal hCG-related molecule in pregnancy urine in the 2 weeks following the missed menses (61% and 50% of total immunoreactivity in the 4th and 5th completed weeks of pregnancy, respectively). Of 15 home test devices, 2 had a detection limit of 6.3 IU/L for regular hCG, but poorer detection of H-hCG. Two devices detected 13 IU/L regular hCG, one with similar detection and one with poorer detection of H-hCG. Ten devices detected 25 IU/L regular hCG, 6 with poorer detection of H-hCG. One device detected 50 IU/L regular hCG, but better detected H-hCG. Overall, 9 of 15 devices did not detect H-hCG as well as regular hCG. Conclusions: H-hCG is the principal hCG immunoreactivity in early pregnancy urine. Home tests vary widely in detection limits for regular hCG (6.3-50 IU/L), and 9 of 15 devices (60%) had poorer detection limits for H-hCG than for hCG. The variation in analytical detection limits appears contradictory to the common claim for all devices of >99% detection of pregnancy on the first day of the missed menses or earlier. We suggest that manufacturers calibrate devices for both hCG and H-hCG and determine the detection rates for pregnancy rather than the proportion of positive results at arbitrary hCG concentrations. © 2001 American Association for Clinical Chemistry.