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Home pregnancy tests: Can you trust the results?

How accurate are the results?

Many home pregnancy tests claim to be 99 percent accurate on the day you miss your period. Although research suggests that most home pregnancy tests don't consistently spot pregnancy this early, the tests are considered reliable when used according to package instructions one week after a missed period. If you need to know earlier, ask your doctor about a blood test.

Could a positive result be wrong?

Although rare, it's possible to get a positive result from a home pregnancy test when you're not actually pregnant. This is known as a false-positive.

You may get a false-positive if you have traces of blood or protein in your urine. Various prescription drugs — including diuretics and promethazine (used to treat allergy symptoms and nausea) — also can cause a false-positive result. Using an expired or damaged test kit may have the same effect.

Could a negative result be wrong?

More commonly, you can get a negative result from a home pregnancy test when you're actually pregnant. This is known as a false-negative. You may get a false-negative if you:

  • Take the test too early. Wait to take the test until your period is at least one day late. That's the earliest most home pregnancy tests can detect pregnancy. For the most accurate results, take the test one week after a missed period.
  • Time the test wrong. If you're collecting urine, do the test within 15 minutes of collecting the sample. And be sure to give the test time to work — but not too much time. You may want to set a timer according to the package instructions.
  • Use diluted urine. Drinking too much fluid before taking the test may cause a false-negative result. For the most accurate results, take the test first thing in the morning when your urine is the most concentrated.

If your period hasn't started within a week after a negative home pregnancy test, repeat the test.

What happens next?

If your home pregnancy test is positive — or if you've taken a few home pregnancy tests and gotten mixed results — make an appointment with your doctor, nurse practitioner or midwife. You may need a blood test or pelvic exam to confirm your pregnancy. The sooner your pregnancy is confirmed, the sooner you can begin prenatal care.

If your home pregnancy test is still negative two weeks after a missed period, check with your doctor. Many things can cause missed periods, including illness, stress, excessive exercise and hormonal imbalances. Your doctor can help you get your menstrual cycle back on track.

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References
  1. Am I pregnant? U.S. Department of Health and Human Services: Womenshealth.gov. http://www.womenshealth.gov/pregnancy/tryingtogetpregnant/amipregnant.cfm. Accessed Sept. 15, 2008.
  2. HCG. Lab Tests Online. http://www.labtestsonline.org/understanding/analytes/hcg/test.html. Accessed Sept. 15, 2008.
  3. Pregnancy tests. U.S. Department of Health and Human Services: Womenshealth.gov. http://www.4woman.gov/faq/pregtest.htm. Accessed Sept. 15, 2008.
  4. Cole LA, et al. Accuracy of home pregnancy tests at the time of missed menses. American Journal of Obstetrics and Gynecology. 2004;190(1):100-105.

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Nov. 1, 2008

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