Evap Lines, and What To Do If You See One

evap lines on a pregnancy test

What’s an evap line?

Evap lines, or evaporation lines, are a fairly common phenomenon that can happen on any kind of urine pregnancy test that isn’t digital. They occur after urine dries, leaving a faint (or not so faint) line behind that can be misinterpreted. What I didn’t realize was that an evap line can look exactly like a positive test result.

How does an evap line happen?

Pregnancy tests are basically tiny chemistry experiments you run on your bathroom counter. Urine travels across a test strip where it has a chance to interact with chemicals that will signal if hCG is present. The tricky part, aside from not peeing on your fingers while you’re doing it, is that you can’t always control for every variable, like for example tiny variances in the individual test strips, or how the urine dries on the paper. Evap lines can form when the ink used to signal a positive pregnancy is pulled into the results window by drying urine, or even just from the dry urine showing up as a faint gray, or shadowy line. It’s important to note that evap lines are different from false positives, even though the rollercoaster you get sent on can be the same.

Are some tests better than others for avoiding evap lines?

The internet has strong feelings about what tests are better overall, but there’s no science to back up if blue or pink dye tests are better for avoiding evap lines specifically. Going digital in this case is probably best, or just not reading the results outside of the testing window. Seriously. Treat it like The Ring. Take that test, regardless of what it says, and get it out of your house. It’s too tempting.

But I want to look, because what if?!

A positive that shows up after the time is up doesn’t count. You can always retest, and if you’re like me and rocking a trusty IUD and NEED TO KNOW THIS VERY SECOND if that evap line is a sneaky positive, you can go to the doctor and get the blood test. But any result read outside of the testing window is invalid.

What do I do if I see an evap line that looks positive?

Retest, either with a new, unexpired urine pregnancy test, or with a blood test at your ob/gyn if there’s a reason, like an IUD, or a suspected ectopic pregnancy. Or just because you need to know. 

Our next reco: 23 Early Signs and Symptoms of Pregnancy

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