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    What Causes a False Positive Pregnancy Test?

    April 26, 2018 / by Center of Reproductive Medicine   

    Center of Reproductive Medicine


    You tried and tried, and finally achieved what you’ve been working towards and hoping for. A positive pregnancy test. You go to the doctor overjoyed, but cautious. You want to be sure this is really happening. Just one little problem. You’re not actually pregnant. What really happened was you had a false positive pregnancy test.

    When you’re already struggling to achieve pregnancy, few things can be as devastating as a false positive. You might be wondering what causes a false pregnancy test to happen.

    Today we’ll explore:

    • All the things that can lead to a false positive pregnancy test
    • What to look for if you think you might be pregnant
    • How to know for sure whether or not you are actually pregnant
    • And more...

    The Most Common Causes of a False Positive Pregnancy Test


    For something that seems so black and white, people often wonder what can cause a false positive pregnancy test. Some of the most common causes are:

    • The pregnancy test being expired
    • Letting the test sit too long before checking it
    • Having a miscarriage or “chemical pregnancy”
    • Being on certain medications
    • Having an ectopic or molar pregnancy
    • Other medical conditions
    • A faulty pregnancy test unit and/or
    • Contaminated samples

    An expired pregnancy test can yield a false positive

    The way that over-the-counter pregnancy tests (also called home pregnancy tests) work, is that they indicate whether or not your urine contains the human chorionic gonadotropin (hCG), or pregnancy hormone. When a pregnancy test is past its expiration date, the chemicals that are inside it don't work the way that they're supposed to.

    Therefore, an expired pregnancy test can misread whether or not your urine contains hCG. Your best bet to avoid this false positive, is to ensure that the test you are taking is not expired. Regardless of where you get it, be sure to check the expiration date that is listed on the packaging before use.

    And as a side note, don't assume that the test you are taking is better or worse than any other based on its price or brand. For example, according to, the tests that you can purchase at dollar stores like Dollar General, were just as effective in indicating whether or not a pregnancy existed, as those of the higher-priced brands found at most big-box stores (Walmart or Target), and convenience stores (Walgreens, CVS, or Rite-Aid).

    What they found: “This test kit is 99% accurate but is not ultra-sensitive in detecting hCG. So, it will not detect low levels of the hormone that are present in your body after fertilization occurs. This is the reason you should wait a few days after missing your period before using the kit. Most experts agree that you get the most accurate results when your period is a week late.”

    Don’t let the test sit too long after completion before checking the results

    The directions on the box are there for a reason. When you allow a test to sit by itself for too long after you’ve completed it, the urine that is on the test can evaporate. As this urine evaporates the test results can be distorted. In fact, one line can suddenly appear as two, or a negative can look like a positive depending on the test you're taking.

    Read all instructions carefully and follow them to the letter. If it says leave the dipstick in the urine for two minutes, for example, take it out at the two minute mark. If the results are available in 10 minutes, don’t wait 20 to check them. You get the idea. Failure to follow the instructions explicitly is one thing can result in a false positive pregnancy test.

    Having a miscarriage or “chemical pregnancy” can lead to a false positive

    For an otherwise healthy woman, she is most susceptible to a miscarriage within the first 12 weeks. A miscarriage is the term used to describe a pregnancy that ends within the first 20 weeks of gestation. However, most miscarriages actually occur in the first 13 weeks, and many women who have a miscarriage never knew they were pregnant in the first place.

    What is a chemical pregnancy? According to the American Pregnancy Association, “Chemical pregnancies may account for 50-75% of all miscarriages. This occurs when a pregnancy is lost shortly after implantation, resulting in bleeding that occurs around the time of her expected period. The woman may not realize that she conceived when she experiences a chemical pregnancy.”

    What causes the false positive in this case is that you still had some hCG in your system when you took the pregnancy test. This is one of the reasons that many experts advise against early detection tests. While chemically speaking the tests are not necessarily wrong in detecting hCG, you may no longer be pregnant when you take the test, unfortunately.

    Certain medications can distort pregnancy test results


    Taking a drug containing hCG can cause a false positive pregnancy test. It takes between one and two weeks for an injection of it to clear your system, depending on the number of units you are prescribed. Therefore, if you are taking injections of hCG as part of your fertility treatments, you would be better off waiting until that period has expired prior to attempting a pregnancy test.

    Other medications that have been found to cause a false positive pregnancy test include:

    • Psychiatric medications such as anti-anxiety (like Xanax and Valium), and antipsychotic prescriptions (like clozapine or chlorpromazine)
    • Diuretics
    • Methadone
    • Anticonvulsants
    • Medications prescribed for Parkinson’s disease
    • Antihistamines
    • Barbiturates
    • Phenergan and other anti-nausea medications

    Effectively, any medication that messes with your body’s chemical makeup, or leaves traces in your urine, could potentially distort a urine test.

    Having a molar or ectopic pregnancy

    In an ectopic pregnancy, a fertilized egg will implant itself somewhere other than the uterus. The most common place is in the fallopian tube, but it can also occur in the ovary, abdominal cavity or the cervix. Because there is a fertilized egg, hCG will be present in the system, resulting in the false positive pregnancy test.

    When an ectopic pregnancy occurs, swift treatment is required to halt the implanted egg’s development. Not doing so can cause significant complications for a woman including loss of reproductive organs, and/or extreme blood loss.

    The symptoms of ectopic pregnancy are:

    • Pressure on the rectum
    • Dizziness, and feeling faint, or even fainting
    • Severe pain on just one side of your abdomen, or in your pelvis, neck and/or shoulders
    • Tender breasts and nausea

    It’s important to note that many of these symptoms can be a sign of a regular pregnancy. On the other hand, if you experience one or more along with the other symptoms, it could be cause for concern. If you even remotely suspect you could be suffering from ectopic pregnancy, do not hesitate. Seek medical attention at once because an ectopic pregnancy is a medical emergency that will only worsen, and can not be managed on its own.

    A molar pregnancy occurs when the fertilization process leads to the growth of abnormal tissue within the uterus. Molar pregnancies rarely involve a developing embryo, but they often entail the commonly known symptoms of pregnancy including a missed period, and severe nausea. With molar pregnancies, hCG is also present in the body, and can therefore lead to a false positive as well.

    Other medical conditions that can cause a false positive include:

    • Urinary tract infection (or UTI)
    • Ovarian cysts and/or ovarian cancer
    • Cancer in the bladder, kidney, lung, colon, breast, liver or stomach
    • Pituitary gland problems, or disorders affecting your hormone levels (although these are rare, they do occur)
    • Blood or white blood cells in the urine stream as a result of kidney diseases or infections
    • Residual hCG in your system from a previous birth, miscarriage, abortion, diet injection programs, or fertility treatments
    • Tumors that produce hCG (again, this is rare, but could happen with things like ovarian germ cell tumors and gestational trophoblastic disease)

    Your pregnancy test unit was faulty

    It’s no secret that pregnancy test units, and their packaging, are mass-produced in factories. Therefore, it stands to reason that one in hundred, or a thousand or even a million could be faulty. While there is no way to guarantee that your test is in perfect condition, that random chance of a faulty test can cause an inaccurate result. It’s one of the reasons that experts agree you should not rely on a single test to determine whether or not you’re pregnant.

    Your urine sample was contaminated

    In some cases, albeit rare ones, a contaminated urine sample can lead to a false positive pregnancy test. Some experts believe that soap, detergents and/or blood in the urine can lead to distorted results. The best bet for avoiding this false pregnancy test is to use a clean sample and sterile conditions.

    For example, if you have to urinate into a cup and then pour it onto the test, you must ensure the cup is sterile, and has no soap/detergents in it. Or, as mentioned above, if you have a kidney disease or an infection such as a urinary tract infection, it can cause blood to be present in your urine which can also affect the test results.

    Is There Such Thing As a False Negative Pregnancy Test?

    If there can be a false positive pregnancy test, you may be wondering if there is such a thing as a false negative pregnancy test as well. Yes. Believe it or not, false negative pregnancy tests can and do occur. Here’s a breakdown of what results can come from a pregnancy test:

    • In the event that you have a false negative pregnancy test, what that means is your test was negative, however you are in fact pregnant.
    • A false positive indicates that you're pregnant even when you are not.
    • A true positive pregnancy test indicates that your pregnant and your results on the test show up as positive.
    • A true negative pregnancy test, just like it sounds, indicates that you are not pregnant, and the test results were also negative.

    How can you know for sure whether or not you are actually pregnant?


    Whether you’ve experienced a false positive pregnancy test or are just curious, at some point you will likely want confirmation as to whether or not you are pregnant. Here are a few symptoms to look for that may help you determine your status:

    • Missed period - perhaps the most common symptom of all pregnancy symptoms
    • A sudden aversion to or craving for certain foods and/or all food
    • A heightened sense of smell
    • Sudden onset fatigue, or increased fatigue compared with previous levels
    • More frequent than usual urination
    • Tender, swollen, or sore breasts (some women even experience tingling, and say their breasts feel heavier or more full)
    • Nausea and upset stomach
    • Bloating
    • Constipation
    • Dizziness and feeling faint or even fainting
    • Mood swings
    • Higher than normal body temperature
    • Headaches and lower back pains

    All symptoms and assumptions aside, however, you’ll ultimately need to visit your doctor for unequivocal proof of pregnancy.

    When you’re ready to visit a doctor, let them know you would like a pregnancy test. They can do one of four things at this point:

    • A urine test
    • A blood test (considered more reliable than a urine test, and can detect a pregnancy earlier than a urine test will)
    • An internal examination (your doctor can perform an internal examination to look for changes to the cervix and uterus. For example, your cervix can change color and become softer, and your uterus can expand even in the first few weeks of pregnancy.)
    • All of the above

    When should you take a test?

    Most doctors and experts agree that you should wait until one full week after your first missed period to take a pregnancy test. Then again, this is the earliest point at which you should test.

    Remember, most miscarriages can occur within the first 13 weeks. It’s important to keep in mind that even if you visit with your doctor and learn you are pregnant, this is not a medical guarantee you will be able to bring the pregnancy to term.

    Want to learn more about pregnancy, infertility, and other things related to these subjects?

    In many cases, reading an article like this can leave people with more questions than answers. We understand that every medical case is different, and you may want to learn more about topics like how best to go about achieving pregnancy, what can lead to miscarriage, causes of infertility, and a variety of other subjects. Check out our blog, the Houston Fertility Journal, to answer many of our frequently asked questions.

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