How JHOME home pregnancy tests work

So how do the tests actually detect hCG? Most of the action takes place along a narrow strip of a special absorbent type of paper. Each strip is pre-loaded with molecules needed to detect hCG and create a colored band and a control band. As urine containing hCG gets wicked up the paper, it passes areas where those molecules have been deposited.

Each test’s design is slightly different, but it generally goes like this: In the first area of the paper the urine hits, dyed antibodies cling to the beta region of hCG, and together, the two molecules flow forward to a second area, where antibodies that cling to hCG’s alpha region are stuck to the paper. These capture the hCG and the dyed antibody, and as the dyed antibodies accumulate, they create a visible line. In the meantime, extra dyed antibody that has not stuck onto any hCG flows on to the control zone, where it gets trapped by a third antibody. It accumulates and creates a visible control line, letting the tester know they used enough urine to make the test work.

In wand tests, all of this happens inside a plastic casing with a handle, and the test zone and control zone are usually under a clear layer of plastic. The urine is picked up by an absorbent material at one end of the wand, either by the tester peeing directly on it (the “stream” method) or dipping it into a cup of urine. The absorbent tip carries the urine to the paper strip inside the wand.

Digital tests work the same way, except they have a sensor that detects the presence of the test line and control line and a screen that displays the results.

Some tests come inside a cassette instead of a wand, much like some at-home COVID-19 tests. The cassette has the same kind of strip inside, but there’s no plastic layer covering the test zone. Instead of an absorbent tip, they have a circular area where the strip is exposed. They come with a dropper you use to transfer a few drops of urine onto the exposed area. You usually have to provide your own cup.

Finally, there are just strips, with no plastic casing at all. They must be dipped into a clean cup of urine. Because they’re exposed, they may be more likely to fail after being in very high or very low temperatures or high humidity.

Any home pregnancy test will have limitations, Dr. Bavan said, so be sure to follow up with a doctor if you get a positive result, or if you have any other questions about testing for potential pregnancy at home. Greene said a blood test is the most accurate and sensitive test for hCG. According to Greene, physicians don’t always automatically order blood tests, though, so if you really need to know very early on, ask for one.