What is a false positive on a pregnancy test?

Woman holding a pregnancy test device
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When taking a pregnancy test you really want to do everything right. You want to be able to have faith in the test and know that the answer you get is the right answer. There is a lot at stake.

What is a false positive?

A false positive on a pregnancy test means that the test detected the hormone hCG in your urine when there really was not hCG in your urine. The newer, more sensitive early pregnancy tests usually detect lower amounts of hCG in the urine, making them more sensitive.

Though there are reasons why you may have a false positive.

What causes a false positive pregnancy test?

For a false positive to be shown on your pregnancy test, you either have hCG in your body for some other medical reason or the test was not working correctly. Call your doctor or midwife for advice on what to do, they may with to do blood work to see if hCG is found in your blood.

The other possibility is that you had a correct positive, in that hCG was found, but that the hCG levels are falling. This is not technically a false positive in the sense that it did detect hCG, but it is false in the sense that you may not have a viable pregnancy. This lower hCG may be a sign of a miscarriage. Either way, you should call your doctor or midwife for advice. They may be able to use certain treatments like progesterone to save your pregnancy.

There can also be instances of lab errors. There can be strange diseases.

This is why you should always follow up with your doctor.

Most doctor's offices use urine tests to test for pregnancy that are very similar to what you use at home. Though they may buy in bulk to get a better price, the technology is essentially the same, but perhaps with a few less fancy plastic wrappers.

If they think that there is 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. This would usually then be repeated to tell what the exact numbers were and whether it was going up or down in the two tests. This can give you a better idea of if you had a false positive or if it was a fluke from the test itself.

If you have had a false positive on a pregnancy test - you will either wait for another cycle to try to get pregnant or will find out later in this cycle that you are pregnant, just weren't pregnant enough at the time of the original test.

"I had a slight positive pregnancy test and went to the doctor," says Clare. "I was really surprised when they said I wasn't pregnant. I felt a bit foolish. Turns out two weeks later - I really was pregnant. One urine test was right, the other wrong."

Source:

Committee on Gynecologic Practice, The American College of Obstetricians and Gynecologists. ACOG. Committee opinion: number 278, November 2002. Avoiding inappropriate clinical decisions based on false-positive human chorionic gonadotropin test results. Obstet Gynecol. 2002 Nov;100(5 Pt 1):1057-9.

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