Home Pregnancy Tests - Is a False Positive Possible?

If you watch the TV show Bones, and saw the episode titled Proof in the Pudding, you may have wondered if it really is possible to get a false positive result on a home pregnancy test. The short answer is no, you can't get a false positive. The long answer starts with the word however. Learn exactly how a home pregnancy test works, and why you can't get a false positive.

A home pregnancy test, whether it is a strip, cassette, or stick test style all do one thing, it tests for a certain amount of hCG (human chorionic gonadotropin) which causes the dye in the window of the test marked with a T to change color. Human chorionic gonadotropin is only produced by a pregnant woman, so it is impossible to get a true false positive pregnancy test when you understand how the test works.

Here is where the answer gets a little more complicated with the word however coming into the fold. There are two times when you could get what appears to be a positive pregnancy test result, but not actually be pregnant. The first circumstance would be if you are undergoing infertility treatment that includes using an hCG trigger shot to induce ovulation. Women are told, or at least should be told, that she should not use a home pregnancy test for at least two weeks, or a full 14 days, after the trigger shot to be sure that there are no traces of the hCG trigger left in the system. If a women gets impatient and tests only 9 days after the trigger shot, it is fully possible that the home pregnancy test would have a positive result but that she may not actually be pregnant.

Even though it is very difficult not to test when undergoing expensive infertility treatments, any woman that is using an hCG trigger must do everything she can to keep herself from testing until at least 14 days after the trigger. There is nothing worse than thinking that you finally succeeded only to find out that you tested to early and there was still some hCG from the trigger in your system.

The only other way that you might end up with what appears to be a false positive home pregnancy test is if you wait too long to read the test results and end up seeing an evaporation line that looks like a positive line in the test window. All home pregnancy tests come with directions that state the test results need to be read within a certain time frame, usually 3 to 5 minutes after completing the test. If the test results are read after 5 to 10 minutes an evaporation line might be seen, and can by interpreted as a positive result instead of what it really is.

So ladies, the next time you take a home pregnancy test be sure to read all of the directions of the test, make sure that if you did use an hCG trigger shot, that enough time has passed and by all means, don't dig the test out of the trash to "double check" the results. If you get a positive result within the tests time frame, congratulations, you are pregnant.

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