What Causes a False Positive on a Pregnancy Test?

If you're taking a pregnancy test, you want to be sure you can trust the results. Thankfully, the vast majority of the time, an at-home pregnancy test result will be accurate. In fact, studies show that when done correctly, these tests are around 99% correct, but there's also the possibility of false negatives and false positives.

While a false positive pregnancy test result is uncommon, it can happen for a variety of reasons. Learn more about the causes of false positive pregnancy tests and what to do if you think you got a false positive on a pregnancy test.

Possible Causes of a False Positive Pregnancy Test

For a false positive to be shown on your pregnancy test, you either have hCG in your body for a medical reason other than pregnancy, or the test was not working correctly.

Call a health care provider for advice on what to do if you get a positive result but know or suspect that you're not pregnant. They may wish to do blood work to see if hCG is found in your blood or conduct other testing to rule out certain health issues.

Here are a few reasons for a false positive pregnancy test.

Test error

While rare, the home pregnancy test you're using could be faulty. It's possible the test wasn't stored properly or was damaged by heat or water. There could also be a defect due to a manufacturing issue, but again, this is rare. Keep in mind that pregnancy tests can also expire.

More likely, although still uncommon, the error could be due to taking the test incorrectly. For example, you could have waited too long to read the results or you could be misinterpreting the test strips, which sometimes have faint lines, called evaporation lines, that can show up even with negative results. True positive results will show up as bright lines.

Early pregnancy loss

Another possibility is that you had an accurate positive result, meaning that hCG was found in your urine, but that the hCG levels are falling. This is not technically a false positive in the sense that the test did detect hCG, but it's a false result in the sense that you may not have a viable pregnancy.

This lowering hCG may be a sign of a miscarriage or a chemical pregnancy, which is when an embryo doesn't implant or grow. You may also still have hCG in your body after a recent abortion.

Ectopic pregnancy

You can also get a positive pregnancy test result with an ectopic pregnancy, which is also known as a tubal pregnancy. An ectopic pregnancy is when an embryo implants outside of the uterus. Unfortunately, these pregnancies aren't viable and treatment is required to remove the embryo to protect the health of the pregnant person and their fertility.

A positive result with an ectopic pregnancy isn't a true false positive as you are actually pregnant, but the pregnancy can't continue.

Certain medical conditions

There are a variety of medical issues that may cause a false positive result. For example, a positive pregnancy test can sometimes indicate a molar pregnancy, a type of non-cancerous tumor that's also known as a hydatidiform mole. Other possibilities include having a urinary tract infection, certain types of ovarian cancer, and kidney disease.

Certain medications

Some medications can create a false positive pregnancy test result as well. These include some anticonvulsants, anti-anxiety drugs, antihistamines, diuretics, chemotherapy medications, antipsychotics, drugs that treat Parkinson's disease, and methadone.

You also can get a false positive from certain drugs used to treat infertility, such as "trigger shots" (hCG medications) and other shots used to treat infertility (HMG medications). These include:

• Pregnyl
• Ovidrel
• Novarel
• Menopur
• Pergonal
• Repronex

When using hCG drugs, you should wait at least two weeks before getting tested so that the injected medication can be fully cleared from the body. Most doctors, however, advise against home testing and ask that you come to the office to get a blood-based test. While the blood test also detects hCG, it is far more accurate than a home urine-based test.

What To Do When You Get a Positive Pregnancy Test Result

If you get a positive pregnancy test, it's always a good idea to follow up with your doctor—especially if you think it could be a false positive. Most doctor's offices use urine pregnancy tests that are very similar to what you use at home. Though they may not look the same, the technology is essentially the same. Alternatively, your doctor might do a transvaginal ultrasound to visually confirm whether you are pregnant or not.

If they think there's an issue with the urine test you used at home, they may opt to try a urine test in the office, or they may go straight to a blood pregnancy test. These pregnancy tests not only confirm the presence of hCG in the blood but can also measure how much hCG is present.

Health care providers often have you repeat the blood pregnancy test a few days later to determine whether your hCG level is going up or down. This series of tests can give your health care provider a better idea of whether you had a false positive pregnancy test result or it was a fluke from the test itself.

What Happens After You Get a False Positive Test Result?

If you've had a false positive on a pregnancy test, that means you got a positive test result but aren't pregnant. If you and your health care provider are unsure what caused the false positive result, they may suggest additional testing to determine the cause.

• If the false positive result was due to a faulty pregnancy test or misreading, you may consider using a digital pregnancy test to confirm your results. These give a clear "pregnant" or "not pregnant" and help avoid confusion due to faint lines. Always be sure to follow the test's instructions to ensure your results are as accurate as possible.
• If the false positive result was due to a medical condition or medication, you may need treatment or a review of your medications.
• If the false positive was due to an early pregnancy loss or ectopic pregnancy, discuss treatment options with a health care provider.