Evaluation of a semi-quantitative pregnancy device for susceptibility to interference caused by hCGβcf

Abstract

Objective: Previous work has documented the ability of the Clearblue Advanced Test with Weeks Estimator, a new over-the-counter (OTC) urine hCG device, to accurately estimate weeks since ovulation in early pregnancy. In this study, the performance of this device in more advanced pregnancy was assessed.

Methods: The Clearblue Advanced Test with Weeks Estimator device was used to test solutions containing purified intact hCG and hCGβcf at concentrations consistent with early, middle and late pregnancy. Urine samples from three normal pregnant patients 9-13 weeks of gestation and from a patient 12 weeks of gestation known to generate false negative results on qualitative urine test devices due to excess hCGβcf were also evaluated.

Results: The Clearblue Weeks Estimator device gave expected results using solutions containing purified intact hCG and hCGβcf at concentrations observed throughout pregnancy. The device generated expected results using urine from three of four patients tested between 9 and 13 weeks of gestation. However, when urine from a patient with elevated concentrations of hCGβcf was used, the device correctly indicated pregnancy although the estimate for the date was incorrect.

Conclusion: This device gave expected "pregnant" results using all samples tested. However, the "Weeks Estimator" should be interpreted with caution when used by patients after seven weeks of pregnancy.

Keywords: False negative; Human chorionic gonadotropin (hCG); Ovulation; Pregnancy duration; hCG beta core fragment (hCGβcf).