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Despite claims that the home pregnancy test is 99 percent accurate marketing, research over the past decade have shown that up to 5 percent of their return false negatives.

Every year, women in the US relies on some 20 million of these tests.

Constructor pregnancy tests suggest that the tests taken on the first or second week after conception can be inaccurate because the hormones of pregnancy may not have risen high enough to be detected.

"the worst [test] gives a false negative in 5 percent of pregnant women tested urine samples."

But Ann Gronowski, professor of pathology and immunology, and of obstetrics and gynecology at Washington University School of Medicine in St. Louis and medical director of the service core laboratory at the Hospital Barnes-Jewish, found that pregnancy tests can also g ive the result was wrong with the woman five weeks or more into their pregnancy, when hormone levels tend to be very high.

He published his first paper that describes this problem in 2009, and has since continued to study and raise the alarm about the serious but under-recognized problem is. , Most recently, he and his colleagues published a paper in the journal, where they evaluate how likely some devices pregnancy is to give a false negative result

Here, he discusses the findings:

How do you find that some pregnancy tests produce false negative results?

About a decade ago, a woman came to the emergency department said she was pregnant and cramping and spotting-which can be a sign of miscarriage but we gave her a pregnancy test at the hospital came back negative. She was sure she was pregnant, so we did blood tests and ultrasound, both of which confirmed she is pregnant.

Shortly thereafter, we had the same experience with the second patient, and at almost the same time a colleague at Vanderbilt University called me the same observation. So we started investigating, and we published a paper describing the problem and its causes.

Why pregnancy tests sometimes return false negative results?

We are using some sort of emergency pregnancy tests that are similar to what you can buy at the drug store. This test detects the pregnancy hormone called human chorionic gonadotropin (hCG) in urine samples. One capture antibody hormone in the urine, and other services as a signal. It has a color that becomes visible when it detects the correct hormones. That blue or pink line the second you see on the test, and it showed positive results (the first line is only there to show the device is working properly).

But the degraded form of the hormone can also be found in the urine, and in some devices the first antibody will bind degraded form. Number of degraded form, called hCG core fragment, rising as the pregnancy advances. The more fragmented hormone that is around, the more likely it will catch the first antibody fragment not intentionally intact hormone. However, antibody fragments do not respond to signals that do not change color when it occurred, and therefore you get a negative result even though the hormone may be present.

How common is this problem?

It depends on the device. They all use a different antibody, and some are better at distinguishing hormones full of fragments of the others.

We look at 11 hospital pregnancy test most commonly used to see whether they are susceptible to false negative current high levels of the hormone fragment. Seven somewhat vulnerable, two are particularly vulnerable, and only two tests that are not vulnerable. The worst give false negatives in 5 percent of pregnant women tested urine samples. That, unfortunately, our tests use when patients are beginning to come. Based on our research, we have switched to a test that does not have this false negative problem.

Do maker pregnancy tests do nothing to solve this problem?

Based on our work, the Food and Drug Administration has recognized the need for pregnancy tests are not prone to false negatives. The FDA requires that all new tests yield a positive signal even when high concentrations of the fragmented hormone. Unfortunately, this requirement not apply to tests that have been approved by the FDA.

What can a woman do if they think that they are receiving a false negative on a pregnancy test?

What is interesting is that some women found our research and have been posting on forums pregnancy online, saying that if you think you are pregnant, but the tests came back negative, dilute the urine with water and try again because sometimes test wrong. And that really can work. Dilution reduce the levels of the hormone enough the first antibody fragment that is more likely to detect the intact hormone anymore.

But I do not recommend it. The best test for detecting pregnancy is a blood test. If there is any doubt, I would recommend that women talk with their doctor and request a blood test

Source :.

DOI :. 10.1373 / clinchem.2018.293076

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