Pregnancy tests detect the presence of a specific hormone that is produced by a woman's body when she becomes pregnant. This hormone is human chorionic gonadotropin or hCG. While you can rely on the results of most pregnancy tests, there are occasions when a pregnancy test may give you a false positive result.
Definition
A false positive pregnancy test result is one where the test detects the presence of hCG, giving a positive result, but in fact you are not pregnant. False positive pregnancy test results are rare. False negative results, when a test does not detect the presence of hCG but you are pregnant, are also possible, especially if your hCG levels at the time you are testing are too low to be measured by the test you are using.
Early Miscarriage
It is possible to get a positive pregnancy test when your period is late only to have your period begin shortly thereafter. This does not necessarily mean that the test result was a false positive. You may have conceived but suffered an early miscarriage. Such early miscarriages are sometimes called chemical pregnancies. If you have physical symptoms that lead you to suspect an early miscarriage, talk with your doctor.
Considerations
There are several possible causes for a false positive pregnancy test result. Certain fertility medications contain hCG and can produce a false positive test result. If your urine sample is contaminated by soap or blood, you could receive a false positive result. If you have recently been pregnant or suffered a miscarriage, a test could pick up hCG remaining in your body from the previous pregnancy. A test that is expired or damaged could produce an inaccurate result.
Evaporation
As urine evaporates from a pregnancy test, it may leave behind an evaporation line, which can be confused with a positive result. It is important to follow package directions regarding the correct time frame for reading test results. Ignore any lines that develop after that time frame has elapsed.
Warnings
Certain cancers can produce hCG in the body which can lead to a false positive pregnancy test result. In fact, hCG tests can be used to track the progress of treatment for trophoblastic disease. If you have a positive pregnancy test that you believe is false, see your doctor as soon as possible for a thorough evaluation.
