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What Is Pregnancy Test Evaporation Line And How Does It Look Like?

Pregnancy Test Evaporation Line1

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Two colored lines on the home pregnancy test kit indicate that you are pregnant, and a single-colored line indicates you are not pregnant (1). Sometimes, a thin and almost colorless line appears on the strip after the allotted time. This line is called an evaporation line and could mean different things.

In this post, MomJunction explains what an evaporation line is, why it appears, how it is different from a faint line, and how to prevent it.

What Is An Evaporation Line On A Pregnancy Test?

An evaporation line is a slight streak that mimics a positive pregnancy test result. It appears as a second line but does not indicate that you are pregnant. This line appears when you  check the result after the stipulated time or when you take the test incorrectly.

An evaporation line is also likely to appear when the result is negative or if the test is taken too early in your pregnancy. It gives you a ‘false-positive’ result.

How Does The Evaporation Line Form?

An evaporation line forms when the urine on the testing well starts to dry or evaporate. The colorless streak usually develops as a result of the composition of certain urine specimen and might appear regardless of the brand of the kit.

How Common Are Evaporation Lines?

Evaporation lines may appear quite frequently during pregnancy tests, and their appearance might depend on the chemical composition of your urine. Consider taking another home pregnancy test when you are not sure of the results.

How Do You Identify The Evaporation Line On A Pregnancy Test Kit?

Pregnancy test kits are convenient to use and come with instructions. As the procedure is simple, you may feel tempted to use it without reading the instructions. However,  you should read the instructions and follow them correctly because even subtle changes can influence the result.

A test result may take two to five minutes to show, depending on the kit. You need to read the results within the reaction time before the urine dries completely. You may get false-positive results if you read them beyond the reaction time (2).

Difference Between The Evaporation Line And Faint Positive Line

Evaporation lineFaint positive line
Time of displayAppears anytime beyond the stipulated time—It could be two minutes, five minutes, or beyondAppears within the stipulated time (depends on the brand’s recommendation)
ThicknessThinner than the control lineSame thickness as that of the control line
ColorUsually colorless and may not be detectableColor is similar to the control line

What Color Are Evaporation Lines On Pregnancy Tests?

Evaporation lines are usually colorless. But, some lines may appear light pink or light blue. They are lighter than the control line and may sometimes appear greyish.

How Do You Avoid Getting An Evaporation Line On A Pregnancy Test?

If you allow the test kit to stay for a longer time, you may find it hard to differentiate between an evaporation line and a positive result. You should retake the test within the stipulated time. Know that a faint line on a pregnancy test may not always indicate an evaporation line.

Sometimes, a faint positive result may also appear if you take the test soon after implantation, since the hCG levels are low around this phase (3). It may also appear if you take the test in the later part of the day when the urine is diluted.

What Else Could Cause A Light Line?

A light line may appear due to the following reasons:

  • Diluted urine sample with low hCG concentration
  • Taking the test too early (4)
  • Chemical pregnancy risk where there is not enough hCG to give a positive line

What Should You Do If You See an Evaporation Line?

Evaporation line means nothing, and you may ignore it. It is a result of evaporation of the urine, and if you think it could be positive, you may take another pregnancy test. hCG levels are known to double every 48 hours; therefore, the positive test line may appear darker as the levels increase.

It is always a good idea to consult a medical practitioner to confirm the results with further confirmatory tests.

Frequently Asked Questions

1. How soon do evaporation lines appear?

A pregnancy test may show positive if the line appears within the period as specified by the brand. If the second line appears beyond this time, it could be an evaporation line.

2. Do pink dye tests have evaporation lines?

Irrespective of the dye color in the test strips, evaporation lines might occur if the test is not taken correctly.

3. Can an evaporation line show up within the time limit?

Ideally, an evaporation line does not appear if you read the test result within the recommended time frame.

Using a home pregnancy test kit is a handy way to know if you are pregnant. However, for an accurate result, you should take the test exactly as recommended. If you are unsure of the result,  wait, and then retake the test. Consulting a gynecologist and testing your blood and urine could give you an accurate result.

References:

1. Pregnancy Test Instructions; UNC School Of Medicine
2. Pregnancy; FDA Food and Drug Administration
3. “Tweaking” The Test; University of Utah Health
4. When is the best time to take pregnancy test; The Ohio State University Wexner Medical Center
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