From the Guidelines
A urine pregnancy test is generally accurate for detecting pregnancy, but its accuracy can vary depending on the timing of the test and the sensitivity of the test itself, with most qualitative tests approved by the U.S. Food and Drug Administration (FDA) reporting a sensitivity of 20–25 mIU/mL in urine 1. When considering the accuracy of a urine pregnancy test, several factors come into play, including the concentration of human chorionic gonadotropin (hCG) in the urine, the timing of the test relative to missed menses, and recent sexual intercourse or pregnancy.
- The sensitivity of a pregnancy test is defined as the concentration of hCG at which 95% of tests are positive, and most qualitative pregnancy tests have a sensitivity of 20–25 mIU/mL in urine 1.
- Pregnancy detection rates can vary widely because of differences in test sensitivity and the timing of testing relative to missed menses, with some studies showing that an additional 11 days past the day of expected menses are needed to detect 100% of pregnancies using qualitative tests 1.
- It's also important to note that pregnancy tests cannot detect a pregnancy resulting from recent sexual intercourse, and qualitative tests might have positive results for several weeks after termination of pregnancy because hCG can be present for several weeks after delivery or abortion (spontaneous or induced) 1. In real-life clinical practice, if there is any uncertainty about the accuracy of a urine pregnancy test, a healthcare provider may consider having patients start using contraceptive methods other than IUDs at any time, with a follow-up pregnancy test in 2–4 weeks, as the benefits of starting to use a contraceptive method likely exceed any risk, even in situations in which the healthcare provider is uncertain whether the woman is pregnant 1.
From the Research
Accuracy of Urine Pregnancy Tests
- Urine pregnancy tests measure the levels of human chorionic gonadotropin (hCG) in urine to detect pregnancy 2, 3, 4.
- hCG is a heterogeneous molecule that exists in different isoforms, including intact active hormone, nicked hCG, free β subunits, and β-core fragment 2.
- The measurement of hCG in urine can be affected by the structural heterogeneity of the molecule, which may lead to variations in test results 2, 3.
Factors Affecting Test Accuracy
- The sensitivity and specificity of urine pregnancy tests can be limited by the detection of only regular hCG, and not other variants such as hyperglycosylated hCG 3, 5.
- False-positive or false-negative results can occur due to factors such as early pregnancy losses, heterophilic antibodies, or delayed implantation 4.
- The use of different types of pregnancy tests, including professional laboratory assays, point-of-care tests, and home devices, can also affect test accuracy 4, 5.