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5 Causes For A False Positive Pregnancy Test

Many women depend on the plethora of home pregnancy tests that are available these days. These tests are easy to do and the manufacturers of these packs claim that their tests are 99% accurate. However, research has shown that despite these claims there are around 5% chances that the test may show a false positive test. This means that the test will show that the female is pregnant while in actuality this may not be the case. This is according to various researches that have been done over the last 10 years.[1]

The manufacturers of these test kits state that the test done within the first two weeks after presumed conception may not show an accurate result since the pregnancy hormones in this time do not get high enough to show a positive result. However, according to studies it has been observed that pregnancy tests may also give a false positive test even at five weeks into the presumed conception when the pregnancy hormones in actuality should be at their peak.[1]

There are many factors that may cause a female to get a false positive result during a home pregnancy test. This may vary from hormonal changes to certain medical conditions or taking certain medications. These causes are what have been explained in the article below:[2]

5 Causes For A False Positive Pregnancy Test

5 Causes For A False Positive Pregnancy Test

Some of the causes for a female getting false positive pregnancy test are:

  1. Evaporation Lines: To better understand this factor, it is important to understand how a pregnancy test gives the results. It is vital for the female to read the instructions on the pregnancy kit carefully before using it. Different pregnancy kits have different instructions which make it important to read all the directions of use carefully. In most of the test kits, it will be recommended to read the result within 5 minutes of using the kit and the maximum time limit of reading the result is 10 minutes. A non-digital test kit will show a single line if the female is not pregnant and two lines if she is.[2]

    In case the test result is read after the maximum time limit, it may give a false positive result since the urine will leave an evaporation line which will be similar to the line that will indicate a positive pregnancy test. This often at times will lead the female to believe that she is pregnant when in fact she is not.[2]

  2. Previous History of Miscarriage/Abortion: If a female has had an abortion or a miscarriage and checks for pregnancy a short time afterwards then again the test will be a false positive. This is because even after miscarriage or abortion the pregnancy hormones will still be high in the body causing the result to be faulty. Once a female conceives the body starts secreting beta hCG which is the pregnancy hormone and its level starts to rise. However, after a miscarriage or an abortion this level starts to go down but only very slowly.[2]

    Thus if a pregnancy test is carried out a short time after the event it may often lead to false positive pregnancy tests. It takes anywhere from a week to about a month for the pregnancy hormone levels to drop down to normal. If a test is conducted within this time frame, then it will almost always yield a false positive result.[2]

    In some cases, the miscarriage is only partial in that there are some tissues left behind from the pregnancy in the uterus which will continue to secrete pregnancy hormones causing false positive pregnancy tests. Thus after a miscarriage a dilatation and curettage is done to clear the uterus of any debris remaining from the pregnancy.[2]

  3. Molar Pregnancy: This is yet another cause for a female to have a false positive pregnancy test. This condition results due to genetic abnormalities during the time of conception resulting in the pregnancy turning abnormal. Molar pregnancy can be partial or complete. In a complete molar pregnancy there is complete absence of the chromosomes of the female and only male chromosomes are present. This leads to complete absence of the development of embryo or placenta.[2]

    In a partial molar pregnancy, the female will have placenta and embryo. However, instead of one set of chromosome from the male and one set of chromosome of female, the embryo will have two sets from the male and just one set from the female causing genetic abnormality. It causes abnormal growth of the embryo and placental tissue. This also leads to the female having a false positive pregnancy test. This condition requires dilatation and curettage for complete cleaning of the uterus.[2]

    It is vital for the beta hCG levels of the female with molar pregnancy be monitored after the procedure to ensure that they return back to the normal levels. At times, the embryo and the placental tissues from a molar pregnancy continue to grow. This is medical referred to as trophoblastic disease and is an emergent medical condition. This will require surgery to completely remove the uterus.[2]

  4. Medications: In some cases, taking certain medications can also result in a female having a false positive pregnancy test. These medications generally have Beta hCG as one of their ingredients. The medications are normally given for treating infertility. The medications cause the levels of this pregnancy hormone to rise up resulting in a false positive pregnancy test. It should be noted however that medications for other conditions do not affect the results of a pregnancy test.[2]

  5. Medical Conditions: There are also certain medical conditions that can result in a false positive pregnancy test. Conditions where the pituitary gland is affected may result in significant rise in beta hCG levels resulting in a female having a false positive pregnancy test. This is usually seen in perimenopausal and menopausal females. Certain forms of cancers that affect the ovary, liver, kidney, or lung also may lead to significant rise in beta hCG levels causing false positive pregnancy tests.[2]

    In female who have a history of ovarian cysts there may be a significant rise of the pregnancy hormone causing her to have a false positive pregnancy tests. Females with frequent UTIs or renal dysfunction also tend to have high beta hCG levels.[2]

In conclusion, as stated by the United States’ Office for Women Health home pregnancy test kits give 99% accurate results if they are done properly according to the instructions provided on the label. However, various studies have concluded that there may be a discrepancy of about 5% where the results may be false positive.

However, if the test is done within the time frame specified by the manufacturer of the test kit then the results are generally accurate, especially if they are done after missing a period.[1,2]

Studies suggest that taking a test immediately after conception may not give the right result since it takes time for the beta hCG levels to rise. In some cases, it has been shown that false positive results are observed even at five weeks where the test results are false positive. It may be due to various factors that impact the results if a pregnancy rest.[1,2]

If a female has a history of miscarriage or abortion then the levels of beta hCG may be high for some time after the event. Thus if a test is conducted during this time then it will yield a false positive result. Similarly females with a history of ectopic pregnancy or a molar pregnancy will also have high levels of beta hCG and will have a false positive pregnancy test results.[1,2]

Proper treatment of these medical conditions is required will dilatation and curettage to increase the chances of the female getting pregnant again. Additionally, conducting the pregnancy test according to the instructions is a must to avoid getting false positive pregnancy test results.[1,2]

There are also certain medical conditions like ovarian cysts or conditions that affect or damage the pituitary gland can also affect the levels of beta hCG in the body. This again causes a female to have a false positive pregnancy test results. People with a history of cancer of the ovaries, kidneys, lung, or liver also tend to have high levels of beta hCG causing them to have false positive pregnancy tests. It is essential to rule out these conditions as a contributing factor in people who are at risk in them having false positive pregnancy tests.[2]


Also Read:

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:November 2, 2021

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