Background: Currently, 20 IU/L is the accepted sensitivity of over-the-counter (OTC) hCG pregnancy tests, and the only sensitivity permitted for point of care (POC) tests. These sensitivity limitations cause significant numbers of false-negative tests, which mislead women and cause them to avoid precautions needed to avoid fetotoxic drug or alcohol damaged pregnancies. A large clinical trial is needed examining background hCG (hCG levels in absence of pregnancy) and determining whether sensitivities can be improved to avoid false negative detection.
Methods: Daily urine samples were collected prospectively from 126 women over 1-7 non-conceptive menstrual cycles and from 68 women while achieving pregnancy. Additional urines were collected from women peri- and postmenopause. A total of 11,991 urines were collected and tested for total hCG and LH.
Results: The upper reference limit for background ranges in the field of clinical chemistry is the 97.5th percentile. Considering the menstrual cycle, the 97.5th percentile of background hCG results was 1.0 IU/L. Including cycles with early pregnancy losses raised this percentile to 1.1 IU/L. Considering also that 10% of tests involve peri-menopausal women, the 97.5th percentile of background results increased to 1.2 IU/L.
Conclusions: The 97.5th percentile or background cut-off was 1.2 IU/L. As such a test with sensitivity 1.2-5 IU/L may be appropriate for urine pregnancy testing. An OTC or POC test with a sensitivity in this range will detect 98% of pregnancies close to the time of missing menses, helping prevent fetotoxic pregnancies or retarded babies.