In an emergency room setting, pregnancy tests are run on women in their reproductive years to rule out pregnancy before care is provided that could endanger the fetus, including X-rays and certain medications. The emergency room pregnancy test is often referred to as a point-of-care (POC) urine test. POC tests are relatively accurate, but even low numbers of false negatives are important considering the large number of overall tests run each year. A rash of latter first trimester false negatives lead researchers to investigate the potential cause of POC issues. The results of the research were published in The Journal of Emergency Medicine.
According to researchers, higher hCG levels in the latter weeks of the first trimester could overpower the POC tests causing false negatives. Variances among POC tests could also pose a problem. POC test manufacturers need to focus on eliminating lot-to-lot variances, which could help eliminate the number of false negatives reported each year.
A false negative pregnancy test could lead to dangerous consequences if the patient is pregnant. Radiation and medications can cause fetal harm and possibly fetal death, but there are maternal issues to consider as well. If ectopic pregnancy is the cause of health issues presented in the emergency room, a false negative POC test could affect treatment and/or increase risk of maternal death.
POC urine tests are clinically designed to detect early stage pregnancy. Late stage first trimester pregnancy can overload the urine test causing a false negative. Manufacturers need to take the clinical use of POC tests into consideration when labeling and manufacturing tests. Labeling tests as viable only in the first weeks of pregnancy or changing the antibodies to include late stage first trimester pregnancy are viable options to reduce the number of false negatives.
Source: Richard T. Griffey, MD, MPH, Caleb J. Trent, MD, Rebecca A. Bavolek, MD, Jacob B. Keeperman, MD, Christopher Sampson, MD, Robert F. Poirier, MD. "Hook-Like Effect" Causes False-negative Point-of-Care Urine Pregnancy Testing in Emergency Patients. J Emerg Med. 2013;44(1):155-160.