Providing a superb example of the ever-changing biomedical landscape for even the most mundane of diagnostics, researchers at Washington University School of Medicine find that some commonly-used urine pregnancy tests lose their negative predictive values after five to seven weeks due to the interference of a variant of the pregnancy hormone human gonadotropin ((hCG)).
A false negative result poses risks to pregnant women who may undergo x-rays, take certain contraindicated medications or have ectopic pregnancies.
Easy-to-use visually-interpreted pregnancy tests have been used by women and clinicians alike for decades. All hospitals offer them.
Two tests, Genzyme's (SNY) OSOM and Cen-Med's Elite were so inhibited that they pose an unacceptable risk of false negatives.
The researchers suggest that manufacturers revise their products' labeling while they refine their tests to account for the interference.
Only urine samples present the risk because the hCG variant is not present in serum.