Table of ContentsView AllTable of ContentsHow Pregnancy Tests WorkDifferences in ResultsHow Common Are Evap Lines?Most Accurate Test ResultsNext Steps
Table of ContentsView All
View All
Table of Contents
How Pregnancy Tests Work
Differences in Results
How Common Are Evap Lines?
Most Accurate Test Results
Next Steps
A faint colored line on apregnancy testmeans you’re pregnant. The line may be light because the urine was diluted or it’s early in your pregnancy.
If you wait more than 10 minutes to check your results, you may see a colorless or gray line in the window. This is an evaporation (evap) line that appears after your urine has dried on the stick. Sometimes evaporation lines and faint positive pregnancy test lines can appear similar.
This article explains the differences between a positive pregnancy test and a result with an evap line, and reviews next steps if you think you’re pregnant or are still unsure.
HUIZENG HU / Getty Images
At-home pregnancy tests check your urine for human chorionic gonadotropin (hCG). Your body releases this hormone when a fertilized egg implants in the lining of youruterus. An at-home test typically involves either urinating on a test stick or dipping the test stick into a cup of urine and waiting several minutes to read the results.
Depending on the test, the results may appear as a plus or minus sign, one or two lines, or the words “pregnant” or “not pregnant.”
If one line (the control line, which confirms the test is working) appears on a non-digital test, it usually means you are not pregnant. If your test shows both the control line and a colored line in the test result window, this typically indicates pregnancy.
Pregnancy tests are most accurate when taken after you have missed a period. Someat-home early pregnancy testscan be used to detect a pregnancy up to 10 days before a missed period, but these results are less reliable.
Differences Between Evaporation Lines vs. Faint Positives
An evaporation line is a faint, colorless line that appears in the results window of an at-home pregnancy test. An evaporation line may appear if you’ve waited too long to read the results of the test.
Sometimes evaporation lines and faint positive pregnancy test lines can appear similar, especially if you don’t know exactly what you’re looking for. Because of this, you may mistakenly assume that you are pregnant when you are not.
Does an evap line mean pregnancy?An evaporation line does not indicate pregnancy. The safest bet is to take another test and read it within the specified time frame for the most accurate reading. Check with a healthcare provider if you’re still unsure about the results.
Does an evap line mean pregnancy?
An evaporation line does not indicate pregnancy. The safest bet is to take another test and read it within the specified time frame for the most accurate reading. Check with a healthcare provider if you’re still unsure about the results.
Color
It’s helpful to take a closer look at the line’s color. Is the faint line 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, it’s 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, evaporation might be to blame.
How Long It Takes to Appear
Many at-home pregnancy tests suggest reading the results within two, five, or up to 10 minutes after urinating on the stick. When urine sits on the test for too long past the recommended time, it can cause an evaporation line.
If you’re checking the result and see two lines during the manufacturer’s stated time frame, it’s more likely to be a faint positive result. But if you wait too long after the reaction time to interpret the results (tests are meant to be read while the strip is still damp), it’s probably an evap line.
How Dye Works in a Pregnancy Test
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 if the urine being tested has diluted and dried.This line can appear in the minutes after the recommended testing time has passed. This is why it’s important to read your pregnancy test within the time frame noted on the product’s instructions.
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:
Though many pregnancy test manufacturers market their products as extremely accurate, research suggests that real-life situations (e.g., errors in the date of an expected period, certain medical conditions, or being peri- and post-menopausal) affect the accuracy rate.
Next Steps After a Faint Positive Result
You might consider retaking the at-home test to ensure the result if you think a line 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 viaultrasoundorblood 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. After that, call a healthcare provider if your test is positive or if you need more help getting an accurate reading.
9 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Planned Parenthood.Pregnancy tests.U.S. Food and Drug Administration (FDA).Home use tests: pregnancy.MedlinePlus.Pregnancy test.Office on Women’s Health.Pregnancy tests.Ross E.Provisionally pregnant: uncertainty and interpretive work in accounts of home pregnancy testing.Health (London).2018;22(1):87-105. doi:10.1177/1363459317739439U.S. Food and Drug Administration.Guidance for over-the-counter (OTC) human chorionic gonadotropin (hCG) 510(k)s - guidance for industry and FDA reviewers/staff.Liao LW, Chen PH, Tsai SY, et al.Rapid β-human chorionic gonadotropin detection in urine with electric-double-layer gated field-effect transistor biosensors and a handheld device.Biomicrofluidics. 2021 Apr 5;15(2):024106. doi: 10.1063/5.0042522Gnoth C, Johnson S.Strips of hope: accuracy of home pregnancy tests and new developments.Geburtshilfe Frauenheilkd. 2014 Jul;74(7):661-669. doi:10.1055/s-0034-1368589University of California San Francisco Health.HCG blood test - quantitative.
9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Planned Parenthood.Pregnancy tests.U.S. Food and Drug Administration (FDA).Home use tests: pregnancy.MedlinePlus.Pregnancy test.Office on Women’s Health.Pregnancy tests.Ross E.Provisionally pregnant: uncertainty and interpretive work in accounts of home pregnancy testing.Health (London).2018;22(1):87-105. doi:10.1177/1363459317739439U.S. Food and Drug Administration.Guidance for over-the-counter (OTC) human chorionic gonadotropin (hCG) 510(k)s - guidance for industry and FDA reviewers/staff.Liao LW, Chen PH, Tsai SY, et al.Rapid β-human chorionic gonadotropin detection in urine with electric-double-layer gated field-effect transistor biosensors and a handheld device.Biomicrofluidics. 2021 Apr 5;15(2):024106. doi: 10.1063/5.0042522Gnoth C, Johnson S.Strips of hope: accuracy of home pregnancy tests and new developments.Geburtshilfe Frauenheilkd. 2014 Jul;74(7):661-669. doi:10.1055/s-0034-1368589University of California San Francisco Health.HCG blood test - quantitative.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Planned Parenthood.Pregnancy tests.U.S. Food and Drug Administration (FDA).Home use tests: pregnancy.MedlinePlus.Pregnancy test.Office on Women’s Health.Pregnancy tests.Ross E.Provisionally pregnant: uncertainty and interpretive work in accounts of home pregnancy testing.Health (London).2018;22(1):87-105. doi:10.1177/1363459317739439U.S. Food and Drug Administration.Guidance for over-the-counter (OTC) human chorionic gonadotropin (hCG) 510(k)s - guidance for industry and FDA reviewers/staff.Liao LW, Chen PH, Tsai SY, et al.Rapid β-human chorionic gonadotropin detection in urine with electric-double-layer gated field-effect transistor biosensors and a handheld device.Biomicrofluidics. 2021 Apr 5;15(2):024106. doi: 10.1063/5.0042522Gnoth C, Johnson S.Strips of hope: accuracy of home pregnancy tests and new developments.Geburtshilfe Frauenheilkd. 2014 Jul;74(7):661-669. doi:10.1055/s-0034-1368589University of California San Francisco Health.HCG blood test - quantitative.
Planned Parenthood.Pregnancy tests.
U.S. Food and Drug Administration (FDA).Home use tests: pregnancy.
MedlinePlus.Pregnancy test.
Office on Women’s Health.Pregnancy tests.
Ross E.Provisionally pregnant: uncertainty and interpretive work in accounts of home pregnancy testing.Health (London).2018;22(1):87-105. doi:10.1177/1363459317739439
U.S. Food and Drug Administration.Guidance for over-the-counter (OTC) human chorionic gonadotropin (hCG) 510(k)s - guidance for industry and FDA reviewers/staff.
Liao LW, Chen PH, Tsai SY, et al.Rapid β-human chorionic gonadotropin detection in urine with electric-double-layer gated field-effect transistor biosensors and a handheld device.Biomicrofluidics. 2021 Apr 5;15(2):024106. doi: 10.1063/5.0042522
Gnoth C, Johnson S.Strips of hope: accuracy of home pregnancy tests and new developments.Geburtshilfe Frauenheilkd. 2014 Jul;74(7):661-669. doi:10.1055/s-0034-1368589
University of California San Francisco Health.HCG blood test - quantitative.
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