What Is Evaporation Line Pregnancy Test And How It Looks Like

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Pregnancy is confirmed if two colored lines appear on the home urine pregnancy test. A single color line indicates that you are not pregnant (1). The evaporation line on a pregnancy test usually occurs if the test is read after a long time since the urine dries. This may appear as a faint or colorless thin line. The evaporation line is easily distinguishable from the colored lines.

Read on to know about the evaporation line on a pregnancy test, why it happens, how to differentiate it from a faint positive line, and methods to prevent it.

What Is An Evaporation Line On A Pregnancy Test?

An evaporation line is a 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 and read within the stipulated time. You should 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 is a result of evaporation of the urine, and if you think it could be positive, you may take another pregnancy test after 2 days . hCG levels are known to double every 48 hours; therefore, the positive test line may appear darker this time 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.

The evaporation line in pregnancy tests occurs after the stipulated time of reading the result and when the sample is starting to dry up. However, if the result is read after a long period of time, it might make the evaporation line not visible to the eye and affect the credibility of the result. Although home pregnancy test kits are commonly used to check pregnancy, it is advised to consult a doctor or ob/GYN for an authentic diagnosis and result.

Key Pointers

  • If the pregnancy test kit is kept for too long and the urine begins to dry out, the evaporation line will appear as faint pink or blue.
  • It may appear if the test is performed too soon or if the hCG levels are quite low, resulting in a false positive.
  • Ensure to read the results within the recommended time and consult your ob/gyn for confirmation.

References:

MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
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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Dr. Anita Gupta

(MS)
Dr Anita Gupta is currently working in University College of Medical Sciences (Medical School) & Guru Teg Bahadur Hospital, Delhi. She has been practicing as a gynecologist & obstetrician for the past 31 years and as a lactation consultant for 18 years. Dr. Gupta is a fellow of Indian College of Obstetricians and Gynaecologists, and a master trainer and course... more

Shikha Thakur

Shikha is a writer-turned-associate editor at MomJunction. Her core interest lies in writing articles that guide couples through their courtship to marriage and parenthood. She also specializes in baby names. Being a postgraduate in Human Resources, she likes understanding people and their relationships. This reflects in her relationship articles, where she deals with both the rosy and the grey side... more

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