What causes a false positive on pregnancy tests?

Written by melissa reece
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Home pregnancy tests work by determining pregnancy through the detection of the human chorionic gonadotrophin (hCG) hormone. Despite the fact that most home pregnancy tests claim to have high accuracy rates (most claim 99 per cent accuracy), you can receive a false positive (a test that states you are pregnant when you are not). For this reason, it is important to always follow the directions when taking a home pregnancy test. Not following directions is a major cause of a false positive, according to justmommies.com. Read the test within the time limit provided on the instructions (anywhere between two to five minutes). Use a timing device to track how much time has passed instead of just guessing, justmommies.com suggests.

Another issue is "Evaporation Lines." These lines can occur when urine crosses the test strip and briefly changes the colour on the test, which you could misconstrue as being positive. Pregnancy tests should have a watermark that resembles the water mark on the dollar bill, according to justmommies.com. If you have to work hard to see the line, you may have an evaporation line. If you are unsure of your results, take another test.

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hCG Levels Play a Part

Tumours caused by cancer or unusual growths on the uterus are known to produce the hCG hormone. Because of this, certain ovarian or breast cancers may also give you a false positive on a pregnancy test. If you take certain medications, such as Phenothiazine, or are using fertility drugs, you may also encounter a problem while taking home pregnancy tests since some of these drugs include the hCG hormone. If you are taking a fertility shot, make sure the shot has cleared your system before taking the home pregnancy test to prevent a false reading. If your urine has a high level of protein, it may also affect the outcome of a test since protein and blood affect hCG levels.

Things to Remember

Always check the test's expiration date. Tests have to work harder after time to find hCG levels so taking a test past expiration may cause a false reading. The best way to ensure that a test is accurate is to see your doctor.

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