Pregnancy

There are two general areas where false answers can be generated: medical conditions and user-linked problems.

Medical conditions. Only drugs that contain hCG can give a positive result. Such medications (e.g., Novarel or Pregnyl) are usually given by injection. Other fertility medications (e.g., Clomid, Pergonal) do not influence hCG levels. If you are taking injectable hCG your GYN should have given you guidelines about when you can test with a HPT. It can take 7-14 days, depending upon the dose given, for the injected hCG to disappear from your body.

There are a few, uncommon, medical conditions which might yield a false positive result. These can include: high levels of LH, and some immunoglobulin antibodies.

The most common medical condition to produce false positive results is a pregnancy that will be lost to very early miscarriage. It is believed that up to 25% of pregnancies are lost in very early miscarriages. Before the advent of super-sensitive hCG tests (and women testing even before a missed period), the loss of pregnancy which did not have an embryo or gestational sac could look like a slightly late period. There might be just enough hCG to trigger a very sensitive HPT, but levels would fall shortly after. This is why we say that it is difficult to judge if a slightly late period was a miscarriage or a late period — one would have had to have a positive hCG test around the time of the bleed to know for sure.

User-linked problems. A test can be very reliable but if instructions are not clear, or if its results are not easy to interpret, one can get a wrong result. In 2009, when 16 HPTs were reviewed for readability, the investigators found that the reading levels ranged from 7th to 10th grade on user instructions, and 11th to college level on the question and answer section. The recommended level for medical instructions is 6th grade reading level. Thus, it may not be surprising that another survey found only 32% of women totally complied with the written instructions on the HPT.

In another experiment, volunteers testing urine in a lab had more accurate results than when actual patients performed tests on their own urine samples. To get around some of these sources of inaccurate results (including evaporation lines and confusing interpretations) manufacturers of HPTs are shifting from manual to digital tests with a built-in monitor reading the results, then giving a simple yes or no.