Evaporation line on a pregnancy test: What to know

Pregnancy tests can be a source of confusion and anxiety for many people. Depending on the type of test you use, many lines and symbols can appear, often leaving people wondering if the result is accurate or not. One of the most common lines people may see is an evaporation line (also known as an evap line), which appears on certain types of pregnancy tests. This blog post will provide an overview of what an evap line is, why it appears and how to differentiate it from a positive result. It will also provide information on what to do if you think the evap line is a false positive. By understanding what an evap line is and how to recognize it, you can feel more confident and prepared when it comes to interpreting the result of a pregnancy test.

How much HCG does a person need for a positive pregnancy test?

Some prenatal tests claim to find pregnancy five or more days before a period is missed. Although they frequently can, the test’s effectiveness is based on the amount of hCG present in the urine.

The average hCG concentration in urine at 9 days after ovulation, or about 5 days before a missed period, is zero, according to 2014 research. 93 milli-international units per milliliter (mIU/ml).

When hCG levels reach 25 mIU/ml or higher, which occurs after ovulation on or around day 11, most early-result pregnancy tests can be used to confirm pregnancy.

By day 14, hCG levels are typically around 137 mIU/ml. However, for some individuals, they can be as low as 45 mIU/ml.

A pregnancy test’s outcome can be impacted if the day of ovulation is off by 1-2 days because hCG increases so quickly in the early stages of pregnancy.

If a person believes they are on day 11 after ovulation, they can typically anticipate an accurate result; however, if they are actually on day 9 after ovulation, the test might not be able to accurately detect pregnancy.

False negatives are more common than false positives. To give the hCG levels a chance to rise if the test is negative, it may be a good idea to retake it in a few days.

Very few medications, including fertility drugs, may cause false positives. Otherwise, a very early pregnancy loss could be indicated by a positive result followed by a negative result a few days later.

Early in pregnancy, there might not be much hCG in the urine, and the positive line might not be very strong. However, even a weak positive line has color, which sets it apart from an evaporation line, which lacks color. Any coloration in a positive line indicates pregnancy.

An evaporation line may appear as a mark on a pregnancy test if:

  • More than 10 minutes have passed since taking the test.
  • The mark is faint and colorless, and it resembles a water spot.
  • The mark has no visible dye in it.
  • The test has failed if the control line on the test does not change color.

    A line on a pregnancy test a positive result if:

  • There is a visible dye in the line, even if the color is faint.
  • The line appears within the period specified on the instructions, which is usually 3–5 minutes.
  • A person has taken an early-result test at least 11 days after ovulation.
  • A person has taken a regular test at least 14 days after ovulation.
  • A person has missed her period.
  • If someone has not followed the instructions on the test’s packaging, evaporation lines may also appear.

    To prevent evaporation lines:

  • Try urinating in a cup before taking the test, then dipping the test in the urine for the duration specified on the box. This technique prevents too much urine from splashing onto the test.
  • Do not use a pregnancy test that has passed its expiration date.
  • Avoid storing pregnancy tests in very hot or cold locations.
  • Check the results within the time frame specified by the test instructions. Evaporation lines and false positives can appear over time.
  • Urine hCG concentrations are often highest when a person wakes up. Taking a test first thing in the morning can increase the chances of an early positive result.

    It can be agonizing to wait for a pregnancy test results. The test is probably positive if the result displays a colored line, no matter how faint it may be. A faint, colorless line may be an evaporation line if the results reveal one.

    Take two tests and closely adhere to the test instructions as this is a straightforward way to help ensure accuracy.

    Those who are uncertain about the results should wait for hCG levels to increase and retest in a few days. This can reduce the risk of false negatives.

    By analyzing the blood or urine, a doctor can deliver the most accurate results.

    Last medically reviewed on July 11, 2022

    What Do Evaporation Lines Look Like?

    Evaporation lines are generally more muted than the control line.

  • On a pink dye test, an evaporation line may look like faded gray.
  • On a blue dye test, the line can appear as gray or even a lighter shade of blue. (Note: For some reason, anecdotally, many mamas find that blue dye tests are more prone to evaporation lines.)
  • Sometimes, though, the evaporation line appears as a colorless streak, almost like an indentation.
  • Additionally, an evaporation line is typically thinner than a control line. As you can see in the image above, the vertical evaporation line is much thinner and has an uneven thickness while the horizontal line is one thickness.

    How long does an evaporation line last?

    Evap lines typically don’t appear every time you take a test and typically only appear after the window of time for reading the results.

    Reading your results within the time specified in the instructions is one way to reduce the likelihood of the confusion that evap lines can bring about.

    Sometimes this is two minutes, sometimes it’s up to 10.

    Evap lines do gradually fade and thin with time, but they rarely completely vanish.

    It is impossible to restore a pregnancy test to its original color after it has become discolored due to an evaporation line.


    How do you tell if it’s an EVAP line or positive?

    A positive result will have a test line that runs from the top of the test window to the bottom with the same thickness and color as the control line. An evaporation line will be a grayish white mark that appears after ten minutes.

    Do all blue pregnancy tests have evaporation lines?

    Evaporation lines are common on pregnancy tests, but they don’t appear every time. It depends on the chemical makeup of each woman’s urine. One of the best ways to avoid any confusion when using a home pregnancy test is to check your results within the reaction time.

    What does an EVAP line look like on blue dye test?

    Evaporation lines are generally more muted than the control line. On a pink dye test, an evaporation line may look like faded gray. On a blue dye test, the line can appear as gray or even a lighter shade of blue.

    Do EVAP lines turn dark blue?

    Do evap lines get darker? Not usually, no. If your line is getting darker, it’s more likely to be either the control line (this is generally the darkest line on a pregnancy test) or a positive result. Evaporation lines on pregnancy tests usually get lighter as your pee evaporates.


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