How Common Is A False Positive Pregnancy Test And What Causes It?

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When you use an over the counter pregnancy test, you expect it to be accurate. In fact, home pregnancy tests are said to have an accuracy rating of nearly 100%.

Why is it then that there are those women who receive a positive reading only to find out later that they are truly not pregnant? If you spend much time on any pregnancy website, you are likely to run into these women and it will leave you wondering if pregnancy tests are really as accurate as they claim to be.

You will find that there are many reasons that a woman may receive a false positive on a pregnancy test. Below you will see the main reasons behind these inaccurate readings and what you can do to prevent a false positive of your own.

1. Improper Testing

If is important, when using an over the counter pregnancy test, that you follow the instructions carefully. Make sure that you read them before you begin using the test. Not only will your instructions tell you the proper way to test, but it will also tell you when the results are no longer accurate.


For example, some tests may display a light positive reading if you read the test after the instructed time. So, it is crucial for you to watch the clock and read the test at the instructed time; guessing how long it has been can lead to results that are not accurate. If you are anxious about the results, which you most likely are, it will be harder to judge the time that has passed.

You also need to avoid looking at the results a second time just to make sure that you read them correctly. Many women who are disappointed about the negative reading may pull the test out of the trash can just to make sure and this often results in a false positive test result. Stick to the time that was instructed.

2. Evaporation Line

There are a few over the counter pregnancy tests that have been said to have what is called an evaporation line. You can see these if you inspect a test closely enough and may even be able to see the line as it briefly changes color when urine runs across it.


The test will need to change color and keep that color at the predetermined testing time. Some specific test, upon further inspection, reveal a watermark, but if there is no color to it or a certain degree of light has been administered in order to see the line, it is best to retest after a few days or to use a digital model instead.

3. Medications

It is also possible that certain medications that women take can cause a false positive on a pregnancy test. For example, phenothiazine, which is found in some anti-depressants, can cause pregnancy tests to be inaccurate.


It is also possible for women who are receiving hCG therapy to have a false positive on their test. It is best, in these circumstances, to visit with your doctor in order to have a more accurate test administered. You urine also can become contaminated with things like blood and protein and result in inaccurate test results.

4. Medical Conditions

You should always seek medical attention if you receive positive results on a pregnancy test so that you will be able to receive the best prenatal care possible. It is also a good idea to see a doctor to confirm a pregnancy because there are actually a few rare medical conditions, such as breast and ovarian cancers can lead to a false positive result. If this is the case, you will need to seek medical attention for these issues.


5. Pregnancy Tests that are Defective

You should always check the expiration date on a pregnancy test before you take one. Taking an expired or faulty over the counter pregnancy test can result in false positive results. Remember that you want to make sure that the results you receive are accurate and therefore it is important that you use quality equipment to make sure the results are the most accurate.


6. Conclusion

If you are uncertain as to whether the results you have received are accurate, be sure and consult your doctor. It is always a good idea to wait a few days and retest just to make sure that you receive the same results, however, if you receive a positive pregnancy test, you should see your doctor either way.

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Regina Ledoux, RN, CNM

Ms. Ledoux began her career as an ObGyn nurse practitioner prior to becoming a practicing midwife in the Santa Cruz community. Working together with ObGyn physicians in her own practice, she has over 20 years experience in women's health, pregnancy and childbirth.