An evaporation line (or evap line) typically appears like a faded streak, while a faint positive test result looks like a lighter blue or pink line, depending on the test dye color.
This article provides an overview of home pregnancy test results.
Differences Between Evaporation Lines vs. Faint Positives
At-home pregnancy tests include what’s known as a control line, which is a line to confirm that the test is working, and a test line, which provides the results. Sometimes evaporation lines and faint positive result lines can appear similar, especially if you don’t know exactly what you’re looking for.
Color
It’s helpful to take a closer look at the line’s color. Is there a faint color to the line that’s the same shade as the control line (usually blue or pink)? This is probably a faint positive result.
If the line appears more “colorless,” like gray, white, or shadowy, this is likely an evaporation line.
Thickness or Thinness of Line
Consider whether the line in question is roughly the same size as the control line. Is it the same thickness and does it run from top to bottom?
If the answer to these questions is yes, even though the line may not be as dark as the control line, it’s likely a faint positive.
If the line you’re looking at is a different size and shape or doesn’t expand across the entire length of the test window, an evaporation line might be to blame.
How Long It Takes to Appear
There’s a reason why it’s important to read your pregnancy test within the time frame that’s noted on the product’s instructions (usually somewhere from three to 10 minutes). When urine sits on the test for too long past the reaction time, it’ll dilute and dry out—causing an evaporation line.
If you’re checking the result during the window, it’s more likely to be a faint positive result. But if you notice the additional line later that day, it’s probably an evap line.
How Common Are Evaporation Lines?
Evaporation lines can be common on home pregnancy tests, but they’re not often discussed.
Cause
An evaporation line happens when the pregnancy test is read after the time frame specified in the instructions.
Many at-home pregnancy tests suggest reading the results within two, five, or up to 10 minutes after urinating on the stick. Checking results after that window means your urine has dried up, potentially causing that streaky evap line.
Getting the Most Accurate Pregnancy Test Results
When taking at-home pregnancy tests, several factors go into getting the most accurate result and avoiding confusion. Experts recommend the following tips:
Check your results within the recommended reaction time window, which will vary slightly by pregnancy test brand. Try a digital at-home pregnancy test instead of a dye-based one if you’re concerned about evaporation lines. Test first thing in the morning because your urine is more likely to have higher levels of hCG at that time. Wait until a day after your missed period to test, even though some pregnancy tests are sensitive enough to detect pregnancy earlier than a missed period.
Next Steps After a Faint Positive Result
You might consider retaking the at-home test to ensure the result if you think it may be a faint positive.
After that, the next step is to check with a healthcare provider to schedule an in-office appointment. They can confirm pregnancy via ultrasound or blood test, if needed, during this visit.
Summary
An evaporation (or evap) line is a slight, typically colorless streak on an at-home pregnancy test that can cause confusion. These lines usually show up when you’ve read the results outside the suggested window and the urine has dried. On the other hand, a faint positive test result will be the same color as the control line—just not as bold or dark. This is more likely to be the case if you look at the test results within the suggested time frame.
If unsure about your at-home pregnancy test results, try testing again the next day. From there, call a healthcare provider if your test is positive or if you need more help getting an accurate reading.
