Characterizing urinary hCGβcf patterns during pregnancy

Elevated concentrations of hCG beta core fragment (hCGβcf) are known to cause false-negative results in qualitative urine pregnancy test devices, but the pattern of urinary hCGβcf during normal pregnancy has not been well characterized. Here, we evaluate the relationship between urine hCG, hCGβcf, and hCG free β subunit (hCGβ) during pregnancy.

Banked second trimester urine specimens from 100 pregnant women were screened for high concentrations of hCGβcf using a qualitative point-of-care device known to demonstrate false-negative results in the presence of elevated hCGβcf 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, hCGβcf, hCGβ, and specific gravity were quantified in these 75 specimens.

Urinary hCGβcf concentrations were greater than intact hCG concentrations at all times. A strong correlation (r(2)=0.70) was observed between urine intact hCG and hCGβcf concentrations. A poor correlation was observed between specific gravity and intact hCG (r(2)=0.32), hCGβ (r(2)=0.32), and hCGβcf (r(2)=0.32). The highest hCGβcf concentrations were observed between 10 and 16weeks gestation but individual women demonstrated very different patterns of hCGβcf excretion.

Urine specimens with elevated hCGβcf are frequently encountered during pregnancy but hCGβcf excretion patterns are unpredictable. Manufacturers and clinicians must appreciate that hCGβcf is the major immunoreactive component in urine during pregnancy and must design and interpret qualitative urine hCG test results accordingly.