Evaporation Line on Clear Blue Pregnancy Test: Is It Positive or Negative?

The whole process of finding out if you’re pregnant is an emotional rollercoaster. It can sometimes be a blessing or even a nightmare if unexpected. There are many pregnancy tests available these days that have made the testing process a lot easier.

It only gets difficult when you don’t know how to interpret the lines on the result. Some typical early pregnancy testing kits used by women include Clearblue, First response, Pregmate, ClinicalGuard, etc.

Although most of the time, these tests are accurate with evaporation line clear blue, sometimes you may see faint lines or rather streaks that may deceive you as a false positive result or an evaporation line clear blue pregnancy test.

How pregnancy tests work

Pregnancy testing can be done using blood or urine. Most of the readily available pregnancy tests are urine-based. Although they come in different brands, they all work on the same principle.

Pregnancy tests are qualitative and rely on detecting hCG at threshold levels. The hCG, aka human chorionic gonadotropin – is a hormone produced only by the placenta to aid in pregnancy.

hCG is a reliable indicator of pregnancy. Its level rapidly but steadily rises during the first few weeks of pregnancy. It reaches peak amounts during the 10th week of pregnancy and slowly declines later.

Usually, these test strips have two windows; one is for control and the other for testing. Once the urine sample has been appropriately placed on the strip, the control window will show an evaporation line clear blue or pink line based on the dye.

evaporation line clear blue

If the control line doesn’t appear, consider the test failed and check for the expiration date and retest.

If the test window shows a blue or pink colored line within 5 minutes, it indicates a positive pregnancy test, even if it is a little faint one. Rarely, you might find other lines or streaks apart from these mentioned.

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Evaporation line clear blue on pregnancy test

A faint and thin streak that appears where the positive line on the strip usually should be is called an evaporation line or commonly known as an evap line. These are formed due to delaying the time of reading the results or wetting the test strip.

Dried-up urine on the strip usually looks like a wet spot. The longer the urine stays on the strip, the higher the chances of forming evaporation lines.

Sometimes, improper technique or expired test strips can also cause evaporation lines.

Evaporation line clear blue is usually colorless or grayish like a wet tissue regardless of the dye of the test strip used.

So, let’s answer the big question, “does an evaporation line on a clear blue pregnancy test always indicate a positive pregnancy”? – No!

An evaporation line on clear blue doesn’t mean a positive pregnancy test unless you took the test too early, used dilute urine, or just used an expired test kit.

In case of an EVAP line, it is advised to repeat the pregnancy test preferably at least 7 days after or best at 3 weeks after the missed period to confirm the test results.

What do evaporation lines look like?

If you’re wondering what an evaporation line clear blue looks like on a clear blue test, here is a clear blue evaporation line example marked by the black arrow.

Courtesy – WeHaveKids

Do evaporation lines disappear?

Evaporation lines do not usually disappear even after 48 hours of testing. They may fade a little over time, but never completely.

If the line fades away, maybe you want to repeat your pregnancy test in a few days to confirm if it was an evap line. You would instead not want to miss out on diagnosing an actual pregnancy.

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Evaporation line clear blue vs positive line clear blue

An evaporation line is like a wet streak on the strip, unlike a positive line that is clearly colored and visibly linear. A positive line is a solid line that can be pink or blue, depending on the kit used.

Even if the line is slightly colored, consider it to be a positive pregnancy test. If you try to retest in a few days, the color gets darker, and the line is more precise.

Evaporation line vs faint positive

A false positive, clear blue evaporation line is not very easily distinguished from a faint positive line. It is common to get confused by an evap line for a faint positive line if you don’t know a clear difference.

A pregnancy test evaporation line on clear blue is colorless, whereas a faint positive line is colored. Don’t be deceived by a light pink or blue line for a grayish evaporation line.

Here is how a faint positive can appear like a faint line but is still colored pink. Usually, when you repeat the test the next day, the line gets darker and more visible, like a positive line.

How to avoid evaporation line clear blue?

To avoid or prevent evaporation, lines follow these steps:

  • Test at least one week after missing period – early period has undetectable level of urinary hCG
  • Use the first morning urine of the day to test – highest levels of hCG in the day
  • Read the results in the right time interval from the test – usually 3-5 minutes
  • Do not dilute the urine sample
  • Follow the right method as per the instructions mentioned on the kit
  • Do not use expired test kits

Blue dye vs Pink dye Pregnancy tests

The pregnancy tests kits come with strips that have specific dye in them. Once the urine sample is placed, a chemical reaction produces either pink or blue lines to indicate a positive pregnancy test along with the control line used as a reference.

Even though they come in different colors, they work on the same mechanism and are effective. The only setback of using blue dye strips is that they have higher chances of getting an evaporation line on clear blue.

EVAP line on clear blue pink dye

The popular opinion is that clear blue-blue dye is prone to forming evap lines, unlike pink dye.

With this being said, many people are misguided about the clear blue–pink evaporation line and believe that pink dye strips do not form evap lines at all, which is a common myth.

Both the dye strips can form evap lines, but the numbers have been reported more in blue.

It is often attributed to blue dye tests due to the similar appearance of a faded blue hue of a faint positive line and the grayish colorless appearance of an evap line.

Does a positive test always mean a normal pregnancy?

Sorry to ruin your moment. Although a positive test indicates a normal pregnancy, a urine pregnancy test cannot precisely determine pregnancy outcome.

Causes of false-positive pregnancy tests or abnormal pregnancy include:

Evaporation line on clear blue confused for positive line – Improper testing technique is  a common cause

Molar pregnancy – also known as the hydatidiform mole, is a condition where no real baby is developing, but the placenta grows, causing an enlarged uterus.

This requires medical attention and removal by a procedure – D&C – dilation and curettage performed by an Ob-Gyn.

During a molar pregnancy, the hCG levels are highly elevated than a normal pregnancy to cause a positive line on the pregnancy test.

Ectopic pregnancy – a condition where the embryo after fertilization gets aberrantly implanted outside the uterus, commonly in fallopian tubes or cervix.

The abnormally implanted embryo still produces hCG. Although levels are not as high as a normal pregnancy, it can cause a positive pregnancy test.

Recent abortion/miscarriage – hCG hormone can tend to stay in your blood for a few weeks following a miscarriage and can cause a false positive test.

If the miscarriage was incomplete – some placental/fetal tissue remains in the uterus and continues to produce hCG.

In such cases, you may be required to get a procedure – D&C – dilation and curettage performed by an ob-Gyn.

Medications – Some medicines are frequently used in infertility and other conditions that can interfere with the pregnancy test results.

Medicines used for infertility containing synthetic hCG can induce ovulation and can also cause false-positive results.

Synthetic hCG containing medicines available include:

  • Pregnyl
  • Profasi
  • Novarel
  • Ovidrel

Other medicines that can cause false-positive pregnancy tests:

What to do if the test result is confusing

It is highly recommended you repeat your test the following day using the correct technique mentioned in the instructions.

The most important part is to read the results in the given period without delay to prevent false positives and confusing results.

Visit your obstetrician or gynecologist to confirm your pregnancy results. You might be ordered to get blood samples for testing if necessary.

This is usually done if the pregnancy is suspected to be still in the early phase. hCG levels are better detected in the blood than in the urine during the early stages of pregnancy.

Sometimes, you may also get a transvaginal or abdominal ultrasound done to determine pregnancy status by detecting the gestational sac and the fetus.

After 6 weeks, the baby’s heartbeat can be seen via a transvaginal ultrasound. It can also help in estimating the age and well-being of the baby.

FAQ

How common are evaporation lines?

An evaporation line clear blue or evap line is a false-positive result. The odds of a false positive pregnancy test are as low as 1% because most of the available pregnancy test kits are 99% accurate.

Do Clear Blue pregnancy tests have evaporation lines?

Unfortunately, yes. Clear blue pregnancy tests can rarely result in evaporation lines. Although evap lines can be seen in both pink and blue dye strips, it is notably of higher incidence in the blue dye strips due to close resemblance of the colors – faint blue and gray.

What does an evaporation line look like on a clear blue test?

The evaporation line on the clear blue test is a faint streak that is usually colorless or grayish that appears where the positive line on the test strip should be.

Can an evaporation line be blue?

No. Generally, evaporation line clear blue are colorless or what they call – grayish like a wet spot on a tissue, regardless of the dye pink or blue used in the test strip.

If you are confident that the line’s color is blue or faint blue, or even pink, repeat your test to confirm the result.

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

EVAP line does not have a color, although it may appear grayish. The evaporation line on clear blue doesn’t disappear with time and tends to remain even after 48 hours of testing.

A positive line is usually colored, maybe pink or blue, depending on the respective dye used in the test strips. Positive lines can be faint but can also get darker with time or disappear as soon as minutes to hours after the test.

What if I accidentally pee on the pregnancy test window?

It happens. But, it is best advisable to repeat the test due to the high chances of inaccurate results by the excess urine altering the results. This may also cause false-positive results in the form of evaporation line on clear blue test strips.

Conclusion

Regardless of what’s to come after that scary pregnancy test, the process is in itself stressful. To add to this, there exists something called an evaporation line, also known as evap lines. 

Evaporation line clear blue is seen at times as colorless faded streaks on the strip for various reasons. They do not mean positive pregnancy.

If you think what you see is an evap line, get yourself retested and seek medical advice. Your doctor can be a better advisor regarding all the evaporation line myths you have heard of.

Now that you have read this post, pregnancy testing is going to be an easy ride. You have got all of it covered. Happy testing!

Dr. Swathi Kilari

Hello there! This is Dr. Swathi Kilari here, a writer in progress. I am a graduate of Cebu Doctors' University from the Philippines and am currently registered to practice in India. I write now and then to share my knowledge and experience about healthcare. I am happy to help you make wise choices to lead a healthy life. Healthcare and teaching are two of my passions. I am a food enthusiast, home baker, and cook. If I am not doing any of these, I am probably sleeping.

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