Characterizing urinary hCGβcf patterns during pregnancy

Objective: Elevated concentrations of hCG beta core fragment (hCG beta cf) are known to cause false-negative results in qualitative urine pregnancy test devices, but the pattern of urinary hCG beta cf during normal pregnancy has not been well characterized. Here, we evaluate the relationship between urine hCG, hCG beta cf, and hCG free beta subunit (hCG beta) during pregnancy. Design and methods: Banked second trimester urine specimens from 100 pregnant women were screened for high concentrations of hCG beta cf using a qualitative point-of-care device known to demonstrate false-negative results in the presence of elevated hCG beta cf concentrations. Additional first and third trimester specimens from the same pregnancy were obtained from 10 women who generated negative/faint positive results, 5 women who generated intermediate positive results, and 10 women who generated strong positive results on the point-of care device. Intact hCG, hCG beta cf, hCG beta, and specific gravity were quantified in these 75 specimens. Results: Urinary hCG beta cf concentrations were greater than intact hCG concentrations at all times. A strong correlation (r(2) = 0.70) was observed between urine intact hCG and hCG beta cf concentrations. A poor correlation was observed between specific gravity and intact hCG (r(2) = 0.32), hCG beta (r(2) = 0.32), and hCG beta cf (r(2) = 0.32). The highest hCG beta cf concentrations were observed between 10 and 16 weeks gestation but individual women demonstrated very different patterns of hCG beta cf excretion. Conclusions: Urine specimens with elevated hCG beta cf are frequently encountered during pregnancy but hCG beta cf excretion patterns are unpredictable. Manufacturers and clinicians must appreciate that hCG beta cf is the major immunoreactive component in urine during pregnancy and must design and interpret qualitative urine hCG test results accordingly. (C) 2016 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.