False Positive Pregnancy Test

False Positive Pregnancy Test

Although rare, false positive pregnancy tests happen to some women. The feeling can leave a woman sad if she was expecting, and relieved if she wasn’t. False positive test results can happen for various reasons, as each test looks for the levels of hCG, or Human Chorionic Gonadotropin in a woman’s urine or blood. When a woman is pregnant, hCG is produced by the developing baby’s placenta. Usually, a woman who’s not pregnant won’t make any hCG. Blood tests can detect lower levels of hCG, so that’s why it’s encouraged a woman sees her health care professional to have this type of pregnancy test done, especially if at-home tests are yielding false positive results. So the question remains, why do pregnancy tests give false positive results?

Causes of a False Positive Pregnancy Test

There are many different reasons why a pregnancy test would yield false positive results. One of the most common reasons why at-home urine tests give false positives is that they were not done properly or the instructions were misunderstood. Certain prescription drugs, including ones a woman is taking for fertility issues such as when trying to fix a Luteal phase defect, can alter results and give false positives. These drugs include:

  • hCG Therapy
  • Phenothiazine
  • Anticonvulsants
  • Anti-Parkinson’s medicines
  • Some tranquilizers
  • Some diuretics
  • Promethazine

Another reason for false positive test results is the possibility of impurities in the urine sample. This could be caused by soap or detergent, blood, etc. Soap and detergent usually come from women who wash the cup that comes in her kit. If you do wash the cup, it’s crucial you remove all soap or detergent before testing. It’s also important to know that these cups are generally sterile and don’t necessarily need to be washed before using. If blood is found in the urine, it doesn’t always mean it’s due to ones menstrual cycle. Women urinate blood for many reasons such as kidney disease or bladder infections. When this happens, it’s possible that the test will yield false positive test results.

Unfortunately, false positive pregnancy test results can also be due to what is called a trophoblastic tumor. Trophoblastic tumors form when something goes wrong with the fertilization of an egg by the sperm. And instead of growing into a baby, the egg grows abnormally and becomes a tumor. This type of tumor is not normal, averaging only 3,000 cases per year in the United States, however when this does happen, the test results give false positives because the tumors that are developed in the reproductive tract produce hCG.

What Do You Do if False Positives Results Happen?

Most experts will recommend taking two tests, both different brands to get more accurate results. Another option is to make an appointment with your health care provider and get a blood pregnancy test done. The important thing to remember is that false positive pregnancy test results are generally rare. If directions are followed correctly on the at-home urine tests, they are said to be 99% effective. But you must follow all directions promptly, including waiting time to check results. Also, performing the test in the morning, using your mornings first urine gives the best levels of hCG. There’s really nothing more you can do if you’ve received false positive results, other than retest or wait it out.

[Page updated November 2013]