How accurate are home pregnancy tests (HPTs)?

Anthony L. Komaroff, MD
Internal Medicine
Home pregnancy tests detect the presence of a hormone in a woman's urine. This hormone, called human chorionic gonadotropin, is normally produced only during pregnancy.

A positive test result from a home pregnancy test is very reliable in confirming that a woman is pregnant. However, getting a negative test result can be less reliable. The accuracy of this test depends on when it was performed. Here's why.

Human chorionic gonadotropin can be detected as early as one week after conception occurs. The timing of conception depends on the timing of ovulation (the release of the egg from the ovary), fertilization (the union of the egg and sperm), and implantation (when the fertilized egg affixes to the uterus). Given all these factors, it is best not to rely on a negative home pregnancy test until at least one week after the time of your expected period.

Human chorionic gonadotropin can also be measured in blood. Blood pregnancy tests are more sensitive than urine tests. If you have any question about the results of a home pregnancy test, follow up with your doctor for a blood test.
A home pregnancy test tells you if a certain hormone -- human chorionic gonadotropin (HCG) -- is present in your urine. This hormone is only produced in women who are pregnant. These tests are correct in about 97 percent of cases. You may get a negative result if you do the test too early, before enough HCG is in your urine. A second test a few days later may be more accurate
Donna Hill Howes, RN
Family Medicine
Home pregnancy tests (HPTs) can be quite accurate. But their accuracy depends upon:
  • How you use them -- Be sure to check the expiration date and follow the instructions. Wait ten minutes after taking the test to check the results window. Research suggests that waiting 10 minutes will give the most accurate result.
  • When you use them -- The amount of hCG or pregnancy hormone in your urine increases with time. So, the earlier after a missed period you take the test, the harder it is to spot the hCG. Many HPTs claim to be 99 percent accurate on the first day of your missed period. But research suggests that most HPTs do not always detect the low levels of hCG usually present this early in pregnancy. And when they do, the results are often very faint. Most HPTs can accurately detect pregnancy one week after a missed period. Also, testing your urine first thing in the morning may boost the accuracy.
  • Who uses them -- Each woman ovulates at a different time in her menstrual cycle. Plus, the fertilized egg can implant in a woman's uterus at different times. hCG only is produced once implantation occurs. In up to 10 percent of women, implantation does not occur until after the first day of a missed period. So, HPTs will be accurate as soon as one day after a missed period for some women but not for others.
  • The brand of test -- Some HPTs are more sensitive than others. So, some tests are better than others at spotting hCG early on.
This information is based on source information from the National Women's Health Information Center.

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