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 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 pregnancy test 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. There is no color change as one would expect.
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, help in early detection, 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 up to ten 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).
However, according to gynecologist & obstetrician Dr. Nisarg Patel, “Even if a pregnancy test turns positive after 10 minutes, it is likely that you are pregnant. But it is important to note that different brands of tests have varying sensitivities when it comes to detecting hCG. Therefore, it may be best to take a second test if it appears positive after 10 minutes to confirm the results.”
Difference Between The Evaporation Line And Faint Positive Line
|Faint positive line
|Time of display
|Appears anytime beyond the stipulated time—It could be two minutes, five minutes, or beyond
|Appears within the stipulated time (depends on the brand’s recommendation)
|Thinner than the control line
|Same thickness as that of the control line
|Usually colorless and may not be detectable
|Color 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 (pregnancy hormone) to give a positive line
What Should You Do If You See an Evaporation Line?
The evaporation line is a result of the 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 such as a urine test, urine analysis, qualitative test, and a medical test for appropriate pregnancy detection.
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. However, anecdotally, blue dye tests have been seen to be more prone to evaporation lines.
An anonymous mother of four shares her experience using a blue-dye home pregnancy test. She says, “A few weeks back, I had a bad experience with an awful blue-dye HPT. I had never had an evaporation line on a pregnancy test before, and despite all my BFP’s, I have had many negative tests in the past. Which is why the blue evaporation line I saw really messed with my head. I mean, come on! It’s even blue! The pink-dye tests I took later confirmed that the blue-dye test was indeed negative (i).”
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.
4. How long does an evaporation line last?
An evaporation line might remain a slight streak for a long time after the test. It might not disappear soon.
5. Does the evaporation line disappear with water?
Evaporation lines usually do not disappear even with water. Hence, if you are unsure about the pregnancy test result, it is advised to use a new kit rather than try to erase the evaporation line and use the same kit.
6. Can an evaporation line show up immediately?
An evaporation line might show up when the result is not read within the stipulated time. This could vary based on the pregnancy test kit.
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.
- 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.
Personal Experience: Source
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
5. Pee is for Pregnant: The history and science of urine-based pregnancy tests; Science In The News; Harvard University
6. Causes of a False Positive Pregnancy Test; Cleveland Clinic