Four reasons for a positive hCG test in the absence of pregnancy

“Why is the pregnancy test positive if she’s not pregnant?”

This is a question I’ve been asked several times and it’s a good one.  The query usually comes from a nurse, doctor, or other healthcare provider after performing a test for human chorionic gonadotropin (hCG) and getting a positive or elevated result that they did not anticipate.

Because hCG is a hormone normally produced during pregnancy, hCG tests are used to diagnose the pregnant patient.  That makes it easy to think of hCG tests as “pregnancy tests.”  While that’s not an inaccurate label for them, identifying hCG tests as pregnancy tests gives the impression that is all they are supposed to do.  Technically, hCG tests are designed to qualitatively detect and/or measure the hormone in urine or blood and there are other reasons besides being pregnant that can cause hCG to be present.

I can think of four different reasons why hCG could be present in a non-pregnant woman.

  1. Biochemical pregnancy.  A biochemical pregnancy occurs when a woman becomes pregnant yet has a spontaneous loss of the fetus before she even knew she was pregnant.  If hCG testing occurs before all of the hCG has been metabolized out of the body then hCG can be detected by a lab test.  This situation is not as uncommon as one might think for two reasons.  First, hCG tests are frequently performed in healthcare settings in order to identify the pregnant patient in order to avoid any medical interventions that are potentially harmful to a fetus.  Second, hCG tests are capable of detecting very low concentrations of the hormone.  The high frequency of testing combined with the analytical sensitivity of the tests means that biochemical pregnancies are easily detected.
  2. Pituitary hCG.  Although the placenta normally produces hCG during pregnancy, it can be made by the pituitary gland.  The pituitary gland is a small structure in the brain that secretes many different hormones that function to regulate many endocrine organ systems.  Interestingly, three hormones normally produced by the pituitary gland (thyroid stimulating hormone, follicle stimulating hormone, and luteinizing hormone) are structurally similar to hCG.  Pituitary hCG is more commonly detected in women greater than 55 years of age but can be detected in women as young as 41 years.  Non-pregnant women with pituitary hCG usually have low concentrations of hCG present in the blood and urine.  Importantly, concentrations of hCG produced by the pituitary gland don’t show the rapid increases that occur during pregnancy.
  3. Malignancy.  Cancer cells sometimes make hCG.  While many different types of cancer have been shown to make the hormone, it’s most commonly associated with the gestational trophoblastic diseases and certain types of germ cell tumors of the testes.  Because testicular tumors occur only in men, the question of detecting hCG in the absence of pregnancy is clearly not relevant.
  4. Interfering antibodies.  Some women have antibodies in their blood that can interfere with hCG tests and cause a positive or elevated result in the absence of hCG.  Only hCG tests performed on blood can be affected by this problem because the interfering antibody molecules aren’t normally present in the urine.  This can be a serious problem because some women have been mistakenly diagnosed with cancer due to the false-positive hCG test result and have undergone unnecessary treatments for it.  The frequency of this problem is difficult to know but it’s probably very low.  Over the last several years, the manufacturers of hCG tests have worked to minimize possible interference from these antibodies but nothing can be done to completely eliminate the problem.  When alerted, the laboratory can help to determine if an hCG test result is falsely positive due to this issue.

So, just because an hCG test result is interpreted as positive doesn’t automatically mean that a woman is pregnant.  There are very valid reasons for detecting hCG in the absence of pregnancy.  That said, when the hCG test result doesn’t match the clinical picture, the laboratory should still be asked that question!  When alerted to the discrepancy, the lab can help to investigate the problem and perhaps shed some light on the cause.

There is quite a bit more to say on each of those four causes but I’ll save those comments for future posts.

 

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5 thoughts on “Four reasons for a positive hCG test in the absence of pregnancy

  1. David Grenache, PhD

    Hanna,

    That’s an excellent question! I should have included “exogenous hCG” in my post as well because when injected at high doses (for ovulation induction or, illicitly, in conjunction with anabolic steroids) hCG can cause positive results.

    However, I know of no published studies that have documented a positive hCG test result in the serum or urine in individuals who are on the fad hCG diet. That doesn’t mean it isn’t possible, it’s just that we don’t know for sure.

    The likelihood of that happening would depend on two things: 1) the route of hCG administration (injected or oral) and 2) the dose of hCG used. The preparations of hCG touted for use in weight loss that I’ve seen don’t contain enough hCG to be detected by hCG tests. Further, most people on the hCG diet consume hCG orally by placing a solution of hCG under the tongue. These preparations are often labeled as homeopathic, meaning they are very diluted solutions of hCG. Even if injected, the amount of hCG in the diet preparations are simply too low to be detectable.

    Several double-blind studies have clearly demonstrated that hCG does NOT cause weight loss. The use of hCG is combined with a 500 calorie per day diet and it is the severe calorie restriction that results in weight loss. These studies have also shown no difference in hunger between individuals who did and did not use hCG while dieting.

    Is it safe? Probably. Although I would be wary of injecting a solution of anything without evidence of properly conducted clinical trials for safety. Notably, the hCG available to dieters is not regulated by the FDA in contrast to the hCG injections used for legitimate purposes (induction of ovulation as part of infertility treatment).

    Thanks for your question!

    David Grenache

    Reply
  2. Hanna Uhrova

    Dr. Grenache,
    Do you know if the new fad of the HCG diet would also cause false positive pregnancy test? And is it really safe?
    Thanks,

    Reply
  3. Alabi Olawale smith

    I came upon this article while on my quest to find an answer to a kind of mystery I came access in my line of duty. Am a biomedical scientist by profession.. i ran a serum HCG on one my client and it came out positive. The lady claimed she hasn't had sex before. I was stunned. I took her urine sample and it showed negative. I further carried out a quantitative beta HCG and it was. 0.6 which is just as low as it could be. I actually ran out of explanation for my client. In a bid to get the right answer.. i find myself here.

    Reply
  4. Concerned

    Is it possible for a women to become pregnant while going through menopause. When I was growing up women going through what they called the change of life, some got pregnant and they called them change of life babies and they were healthy babies, question is why are some health care professionals think that when a woman is going through menopause it is impossible for her to become pregnant. Can you give a reasonable answer.

    Reply
  5. David Grenache

    Although not common, women who are “going through menopause” (i.e. the menopausal transition) can become pregnant. A woman who has stopped menstruating is not capable of achieving pregnancy.

    Reply

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