What is an evaporation line on a pregnancy test strip

Evaporation lines

An evaporation line on a pregnancy test strip is a faint and colourless line that may appear after the recommended time frame for interpreting the pregnancy test results has passed. Pregnancy tests typically have a specified window during which the results should be read (known as the read time), often around 3 to 5 minutes after the pregnancy test is taken.

An evaporation line occurs when the urine on the test area evaporates, leaving behind a residue or mark on the pregnancy test strip. This line can sometimes be mistaken for a positive pregnancy test result, especially if it appears within the time frame for reading the results. However, it's crucial to follow the instructions provided with the specific pregnancy test, as reading the results outside the recommended time frame may lead to inaccurate interpretations.

What is a ghost line on a pregnancy test strip?

Another term for an evaporation line on a pregnancy test strip is a "ghost line." Both terms are used to describe a faint, colorless line that may appear on the test strip after the recommended time frame for reading the pregnancy test results has passed. It's important to note that these lines are typically caused by the evaporation of urine and should not be interpreted as a positive pregnancy result. 

How common are evaporation lines on pregnancy test results?

Evaporation lines on pregnancy test strips are relatively common and can occur with many types of home pregnancy tests. The likelihood of seeing an evaporation line can be influenced by various factors, including the specific brand and design of the pregnancy test, how long it's left to develop, and the concentration of the urine used.

Here are some factors to consider:

1. Pregnancy test design:The design of the pregnancy test can influence the occurrence of evaporation lines. Some tests may be more prone to displaying faint lines after the designated time frame. Evaporation lines are more common with pregnancy test strips as more of the strip is visible.
2. Time frame: Evaporation lines typically appear after the recommended reading time for the pregnancy test, usually within 10 minutes after taking the test. Reading the results outside of this time frame can increase the chances of seeing an evaporation line.
3. Urine concentration: Concentrated urine may be more prone to leaving residue on the pregnancy test strip as it evaporates, potentially leading to the appearance of an evaporation line.

Is there a way to avoid seeing evaporation lines?

While it may be challenging to completely eliminate the possibility of seeing evaporation lines on a pregnancy test, there are steps you can take to minimise the chances or reduce the likelihood of confusion:

1. Always follow the pregnancy test instructions: It is important to always read and follow the instructions provided with the pregnancy test kit. This includes using the test within the recommended time frame for reading results and avoiding extended waiting periods.
2. Use first morning urine: Pregnancy tests are often more accurate when conducted using the first morning urine, as it is usually more concentrated. This can help reduce the chance of faint lines due to evaporation.
3. Set a timer: To avoid misinterpreting the results, set a timer as soon as you take the test. Stick to the recommended reading time and do not check the results after that period has passed.
4. Dispose of the pregnancy test strip immediately: this will avoid the temptation of you looking at the pregnancy test result after the read time.
5. Use a digital pregnancy test: Digital pregnancy tests provide a clear "pregnant" or "not pregnant" result without relying on the interpretation of faint lines. However, these type of pregnancy tests are more expensive than pregnancy test strips.
6. Find a brand of pregnancy test strip that suits you and stick with it: This way you will get used to using the test strips and interpreting the results. Some pregnancy test brands may be less prone to displaying evaporation lines than others. 

Despite these precautions, it's important to understand that evaporation lines can still occur on pregnancy test strips. If you are unsure about the results, it's advisable to take another test or consult with a healthcare professional for confirmation.

Are evaporation lines more common on ultra early detection pregnancy test strips?

Evaporation lines can occur on any type of pregnancy test strip, regardless of whether they are marketed as "ultra early detection" or not. The likelihood of seeing an evaporation line is influenced by various factors, including the design of the pregnancy test, the recommended reading time, and the concentration of the urine used.

The term "ultra early detection" often refers to pregnancy tests that are able to detect pregnancy very early in the pregnancy process, sometimes even before a missed period. These ultra sensitive pregnancy tests are more sensitive to low levels of the pregnancy hormone hCG (human chorionic gonadotropin), but their sensitivity doesn't necessarily make them more prone to evaporation lines.

To reduce the chances of seeing evaporation lines, it's important to follow the instructions provided with the specific test, use first-morning urine when possible, and read the results within the recommended time frame. Evaporation lines are more likely to appear if the results are read after the designated time, and they can be mistaken for positive results, causing confusion.

Remember that proper usage of the pregnancy test, adherence to instructions, and careful timing are key factors in obtaining accurate results.

To avoid confusion, it's recommended to always read the test results within the specified time frame and not rely on any lines that appear after that period. If there is uncertainty about the result, it's advisable to take another test or consult with a healthcare professional for confirmation. Evaporation lines are common and are not indicative of pregnancy, so it's important to always interpret the results according to the test's instructions.

What does a positive pregnancy test strip result look like?

Below are two pregnancy test strip results. The top ones shows a negative result and the bottom one shows a positive result (BFP). Both pregnancy test results were read at the correct read time for the test. 

You may also find our faint line on a pregnancy test information page helpful