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Why Does Pregnancy Test Kits Give You False Positive, & How Do I Know Whether I Am Pregnant?

Updated: Oct 21, 2022

How To Identify An Evaporation Line On A Pregnancy Test?

In early pregnancy, there may be very little hCG in the urine, and the positive line may be faint. But even a faint positive line has colour, and this distinguishes it from an evaporation line, which is colourless. Any coloration in a positive line indicates pregnancy.

A mark on a pregnancy test may be an evaporation line if:

  • More than 10 minutes have passed since taking the test.

  • The mark is faint and colourless, and it resembles a water spot.

  • The mark has no visible dye in it.

If the control line on the test does not change colour, this means that the test has failed.

A line on a pregnancy test a positive result if:

  • There is a visible dye in the line, even if the colour 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.

Evaporation lines are also likely to appear if a person has not followed the instructions on the test’s packaging.

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. TakingTrusted Source a test first thing in the morning can increase the chances of an early positive result.


Waiting for the results of a pregnancy test can be agonising. If the result shows a coloured line, even a faint one, then the test is likely positive. If the results show a faint, colourless line, then this may be an evaporation line.

A simple way to help ensure accuracy is to take two tests and carefully follow the test instructions.

Anyone who is unsure of the results should give hCG levels time to rise and take another test in a few days. This can reduce the risk of false negatives.

A doctor can provide the most accurate results by testing the blood or the urine.

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