If a line on a pregnancy test appears after 10 minutes, it is most likely an evaporation line. However, it is important to note that an evaporation line does not indicate that a person is pregnant.
The line forms as urine dries in the results window. Evaporation lines are usually colorless or gray, are thin and streaky, and only form after the allotted time frame.
According to Parents.com:
“It’s important to read the pregnancy test in the time window recommended by the test kit. Checking the test too early or especially checking it too long after the recommended window may show a false positive evaporation line.”
Urine pregnancy tests are usually meant to be read within three to five minutes of use.
Reading them after that time period can result in an inaccurate result. You should test again, being sure to read the results as directed.
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Evaporation Line on Pregnancy Test
An evaporation line is a line that can appear in the test window as your urine dries.
An evaporation line on a pregnancy test can be identified by its faint, colorless, or gray appearance.
It typically appears after the recommended reading time, often hours later but sometimes as quickly as 10 minutes after testing.
Unlike a true positive result, an evaporation line lacks the distinct color and definition associated with a positive pregnancy test.
It is crucial to adhere to the specified time frame for result interpretation as it is possible to mistake an evaporation line for a positive pregnancy result.
If you see a line appear after the result time window has passed, take another test, following all instructions carefully.
How To Prevent Evaporation Lines
Preventing evaporation lines on a pregnancy test can help ensure more accurate and reliable results.
Here are some tips to minimize the likelihood of evaporation lines:
- Follow Instructions: Always read and follow the instructions provided with the pregnancy test kit.
- Use First Morning Urine: Pregnancy tests are often more accurate when conducted using the first urine of the day. This is because the concentration of hCG is usually higher in the morning.
- Check Expiration Date: Ensure that the pregnancy test kit is not expired. Using an expired test may yield inaccurate results.
- Avoid Overhydration: Drinking excessive fluids before taking the test can dilute the concentration of hCG in your urine, potentially affecting the accuracy of the results. Try to maintain a normal level of hydration.
- Read Results Promptly: Evaporation lines are more likely to appear if you read the results after the recommended time frame specified in the test instructions.
- Use a Timer: Set a timer to ensure you adhere to the recommended waiting time. This can help you avoid misinterpretation of results due to extended waiting periods.
- Use a Midstream Method: Some pregnancy tests allow you to urinate directly on the test strip, known as the midstream method. This reduces the chances of evaporation lines compared to tests where you dip the strip into a urine sample.
- Use Pink or Red Dye Tests: Tests that use blue dye are known for producing evaporation lines after the time frame for checking results.
- Store Tests Properly: Store pregnancy tests in a cool, dry place, away from direct sunlight and extreme temperatures. Storing tests in the bathroom, where humidity levels can be high, might affect their accuracy.
Evaporation Line vs. Faint Positive
An evaporation line won’t always appear, but if it does, it will be after the recommended time for reading the results.
Evaporation lines are colorless, thin, and fuzzy rather than consistent.
They appear on negative pregnancy tests after the time allotted for viewing the results.
Also, you may see the evaporation grow slightly darker as the test sits. Once the evaporation line appears in the testing window, it’s there to stay.
A faint positive line will have a definite color (either pink or blue depending on the test).
Faint positive lines are thicker and more defined than evaporation lines and appear within the time frame for checking results.
Once you have received a faint positive, subsequent testing in the days following should see the line growing darker with each passing day.
| Evaporation Line | Faint Positive Line |
|---|---|
| Colorless or gray, contains no dye | Has a faint but definite color |
| Appears after test time, often hours later | Appears within the time frame |
| Thin and hard to see | Thicker and defined |
| Inconsistent/irregular | Consistent, follows the test line pattern |
| Can darken slightly over time | Will get progressively darker with future tests |
| Does not indicate pregnancy | Indicates the presence of hCG hormone |
Evaporation Line vs. Indent Line
While an evaporation line is associated with extended waiting times, an indent line can be present during the appropriate timeframe but does not confirm pregnancy.
An evaporation line on a pregnancy test is a faint colorless or grayish line that becomes visible after the recommended reading time has passed, typically hours later.
These lines can appear anywhere on the test area and are not specific to the result window.
An evaporation line is not a reliable indicator of pregnancy and should not be interpreted as a positive result; it occurs as a result of the urine evaporating on the test strip.
An indent line is a line that may appear within the recommended reading time on a pregnancy test but lacks the color and definition of a true positive line.
Indent lines are typically found in the result window and can be mistaken for a positive result.
However, indent lines are not indicative of pregnancy and result from the test’s design and the interaction with testing materials.
How Pregnancy Tests Work
Home pregnancy tests work by detecting the presence of a hormone known as human chorionic gonadotropin (hCG) in a woman’s urine.
After conception, the fertilized egg implants into the uterus, and the body starts producing hCG.
This hormone is released into the bloodstream and eventually enters the urine.
A home pregnancy test typically consists of a test strip or absorbent material that is sensitive to hCG.
When a woman takes the test, she either urinates on the test strip or dips the strip into a collected urine sample.
If hCG is present in sufficient quantities, it binds to specific antibodies on the test strip, triggering a chemical reaction.
This reaction produces a visible result, such as the appearance of lines or symbols on the test, indicating whether the test is positive or negative.
The control line serves as a reference to ensure the test is working correctly while the result area indicates the presence of hCG.
How Much HCG Must Be Present
Generally, most home pregnancy tests are designed to detect hCG at levels of 25 mIU/mL (milli-international units per milliliter) or more.
This sensitivity level allows the test to detect pregnancy at an early stage.
In the early days after conception, hCG levels are relatively low, but they increase rapidly as the pregnancy progresses.
How To Take a Pregnancy Test Correctly
Every urine pregnancy test is different, so it’s important to read the directions that come with your test.
However, there are some steps you can follow to help you no matter what test you choose.
- Try to take your pregnancy test using your first urine of the day.
- Read all directions before you start the test.
- Have a timer available so you know when to read your results.
- Pee directly onto the testing stick with the stick pointing down. Make sure to urinate for as many seconds as the test requires.
- You can also pee into a cup, and then dip the testing stick in the urine for as many seconds as the directions say you should.
- Read your pregnancy test within the time window required.
- Do not read your pregnancy test after the time window has passed, and disregard the results if you do.
- Try not to take a pregnancy test before the first day of your missed period for the most accurate results.
Frequently Asked Questions
How Many Minutes Does It Take a Pregnancy Test To Show Positive?
How long it takes for your pregnancy test to show positive depends on how far along your pregnancy is and how high your hCG level has climbed.
Most pregnancy tests will come back positive by the 3-minute mark.
However, one of my pregnancy tests came back bright and positive within the first minute.
Can a Pregnancy Test Change From Negative to Positive?
It may take a couple of minutes for your pregnancy test to change from negative to positive, but it can happen.
However, if you read it after the time frame recommended, you likely aren’t looking at a positive test. You are looking at an evaporation line.
It’s also possible to take a pregnancy test and get a negative result one day and then get a positive result the next day.
The increase in your hCG hormone gets credit for this.
What Time of Day Should You Take a Pregnancy Test?
While you can take a pregnancy test any time of day, first thing in the morning is usually best.
Your urine is more concentrated the first time you urinate in the morning, so it will be easier for a pregnancy test to pick up hCG levels and confirm the pregnancy.
Diluted urine used later in the day can give you a false negative.
Can a Negative Pregnancy Test Be Wrong?
A negative pregnancy test can be wrong, though this is rare and happens only around 5 percent of the time.
One reason you may be getting a negative test when you are actually pregnant is that you are testing too early.
If your hCG level isn’t high enough, the pregnancy test will come back negative, and levels rise as the pregnancy progresses.
You can also dilute your urine by chugging too much water before taking a pregnancy test.
While it’s always a good idea to drink water, it may cause your urine to be so diluted that your hCG levels won’t register a positive result.
Kristy is the mother of four, including identical twins. With a background in education and research, she is constantly learning more about parenting and raising multiples. When she has spare time, she enjoys hiking into the woods with a great book to take a break.