If you’re hoping to be pregnant, a false pregnancy test is a huge disappointment. Although false pregnancy tests are rare, they do happen. Home pregnancy tests measure the levels of a hormone called HCG in the urine. HCG is a hormone produced by a fertilized egg when it implants in the wall of the uterus.
Home pregnancy tests, when used properly, are around 99% accurate, but false positives and false negatives both can happen. A false positive pregnancy test is one where a pregnancy test says you’re pregnant, but you actually aren’t. A false negative is where you are pregnant, but the test misses it.
More accurate than a urine HCG pregnancy test is a blood HCG test. The advantage of a blood pregnancy test is it can detect lower quantities of HCG in the blood and thereby detect a pregnancy earlier.
Causes of a False Positive Pregnancy Test
One of the more common causes of a false pregnancy test is performing or reading the test improperly. If you wait longer than the specified time to read the results, the urine evaporates and can form a line that looks like a positive test. Always check the expiration date of a home pregnancy test too. If it’s past the expiration date, it can yield a false positive result.
Another cause is contamination of the urine specimen you’re using. Soap, household cleaners, etc., can alter the results you get and make it look like you’re pregnant when you’re not. Remember, the cups that come with a pregnancy test kit are sterile, so you don’t need to wash them. If you do, make sure there’s no soap remaining in the cup.
Another reason a pregnancy test can be falsely positive is because you were pregnant, but the pregnancy is no longer viable. If you test early, you may get a positive result because you’re pregnant and then miscarry. The fertilized egg implanted briefly in the lining of the uterus and was then lost. This is called a chemical pregnancy. Experts believe chemical pregnancies are quite common and are often unnoticed. For example, you conceive and quickly lose it around the time of your expected period.
A urinary tract infection can also cause a pregnancy test to be falsely positive. When you have a urinary tract infection, blood and protein can enter your urine and alter the test results. If you have symptoms of a urinary tract infection and get a false positive test, talk to your doctor.
A false positive pregnancy test can also happen if you have an ectopic pregnancy, a situation where the fertilized egg implants in an abnormal area rather than the uterus. Women who have an ectopic pregnancy also usually experience abdominal pain and bleeding. Ectopic pregnancy is an emergency, so see your doctor immediately if you have these symptoms. Very rarely, a tumor that produces HCG may cause a false positive pregnancy test.
Are you taking medications or fertility treatments? Both can cause a false positive pregnancy test. Medications known to cause a false positive pregnancy test include seizure medications, some anti-anxiety medications, medications used to treat Parkinson’s disease, certain types of diuretics, and promethazine. These days, some weight loss clinics offer HCG injections for weight loss. These, too, can give a false positive pregnancy test.
The Bottom Line
False positive pregnancy tests are rare and are often due to performing the pregnancy test incorrectly. You can avoid false positive tests by closely following the instructions and waiting until after the time of your expected period to test.