Estimating the hCGβcf in urine during pregnancy.

Objective: Elevated urine concentrations of hCG beta core fragment (hCGβcf) are known to cause false negative qualitative point-of-care hCG test results, but limited information is available regarding urine hCGβcf. In this study, we evaluate the relationship between serum and urine hCG concentrations and the frequency of elevated urine hCGβcf concentrations.

Design And Methods: Paired serum and urine specimens were obtained from 60 women at various stages of pregnancy and hCG was measured using the Abbott Architect and Roche Cobas e602 assays. Urine specimens with the greatest difference in urine hCG concentrations between these two instruments were tested using a qualitative point-of-care device and hCGβcf was quantified using LC-MS/MS.

Results: Urine hCG concentrations were lower than serum and the magnitude of the difference depended on whether the hCG assay detected hCGβcf. Elevated hCGβcf concentrations (>280,000pmol/L) were observed in 12% of specimens from an unselected patient population. There was a significant correlation (r=0.97; p<0.0001) between the difference (Roche hCG-Abbott hCG) and the hCGβcf concentration as measured by LC-MS/MS (Roche-Abbott difference IU/L=(hCGβcf (pmol/L)∗0.131+656)).

Conclusions: A correlation exists between serum and urine hCG concentrations but this correlation is variable. hCGβcf concentrations can be estimated using two automated assay reagent platforms that differ in their recognition of hCGβcf.