Evap Line Pregnancy Test: Results and Interpretation

Understanding the Truth About Evap Line (Pregnancy Test Results Interpretation)

Evap line. Pregnancy test with this line creates confusion. Is it a positive pregnancy result or not? This faint line on a home urine pregnancy test kit is created when urine in the test area evaporates or starts to dry. Evaporation will leave a colorless, faint line. What a woman will see will be two lines, one dark and another very faint. So, is that considered two lines (meaning positive pregnancy) or one line (meaning negative pregnancy)?

The presence of evaporation lines on a pregnancy test can interfere with correct interpretation if the test is not read within the recommended period. A pregnancy test is to be read and interpreted within 5 minutes. This periodcan slightly vary, depending on the brand,so check the instructions well.

Causes of Evap Lines
An evap line is a residue of urine as it dries off from the test window. This is a very faint line, almost unnoticeable. It is very much like the dried off mark that urine and other liquids usually leave on the surface after evaporation. It is not an indication of HCG hormone reacting with the reagent in the test strip.

It is merely a residue left on the pregnancy test strip after the water in the urine has evaporated. It is similar to a watermark created on a surface when the water has dried up.

An evap line is typically colorless. At times, it can appear greyish or shadowy. As the urine evaporates, it can cause the antibody strip to be more visible, making it look like a faint line.

This line on the pregnancy test kit can cause confusion and inaccurate results if the test strip sits too long before being read. Always read the instructions that come with the home pregnancy test strip and read within the allotted or recommended time.

Evap line pregnancy test does not always appear in each and every test. This is because urine has very unique characteristics and composition among different individuals. Some women may see an evap line within minutes while in others, this line may appear in an hour or so.

This only becomes a problem when women check on the home pregnancy test strip again after a few minutes. These tests kits are meant to be checked within 5 minutes of adding the urine sample into the designated spot on the kit. Some women keep the kit after seeing the negative result and then check on it again after about an hour. This is when confusion results. If the test turns out negative within 5 minutes, then it is negative. Waiting for a few more minutes will not make it a positive result. Instead, some women will get the evap line, which they consider as a positive pregnancy indicator.

Understanding the truth about evap line (pregnancy test results interpretation)
Understanding the truth about evap line (pregnancy test results interpretation) | Source


Do note that a negative or a positive result on a home pregnancy test kit is not a definitive result. So many other factors will give false positive or false negative results. If suspecting pregnancy, always get a checkup with a medical practitioner for more definitive results regardless of the home pregnancy test kit results.

Using and Interpreting the Home Pregnancy Test Kit

Most of the available home pregnancy testing kits require a minimum of 5 minutes of reaction time. This is the time needed in order for the reactive chemicals in the test kit to react with the components of urine.

There are two basic types of home pregnancy test kits. These are the dipstick or the test strip, and a test kit that comes with a test device and a collection cup for the urine.

With the dipstick home pregnancy test kit, one end of the stick is placed right under the urine stream. An alternative is to collect the urine in a small container and one end of the test stick is dipped into the sample. Urine will enter from this end and saturate the test strip. If there is any HCG in the urine, it will be caught by the antibodies in the antibody strip. Once caught, the dye will accumulate in this area as it passes through the strip. This will give the second line, indicating positive pregnancy. If no HCG is present, then there will be nothing in the antibody strip to react to the dye.

The second type of home test kit for pregnancy is using a test device and a collection cup. Urine sample is collected in the cup and the test device is placed into this cup. An alternative is a test kit with a small well on one end. Urine sample from the collection cup is taken using a dropper. A few drops of urine is then placed into this well.

A home kit is pretty reliable, provided that a good urine sample is obtained at the right moment, and the process is done correctly.

The best sample is the first voided urine in the morning. This will give the most reliable result.

The day of urine collection matters. Levels of HCG (if present) depend on how far the pregnancy already is. Early stages (a few days before a missed period) of pregnancy have very low HCG levels because the main tissue producing most of it has yet to fully develop. As the pregnancy develops, HCG levels steadily increase.

The results can be read between 3 to 5 minutes. Readings are more accurate if the pregnancy kit is checked within the reaction time. Beyond that, urine will start to dry off and evap line pregnancy test will start to appear.

During the reaction time, bands will start to appear in the test window of the test kit. These band or bands will show either positive pregnancy or not. A single line means a negative pregnancy result and two lines mean the woman is pregnant. The first line that appears is the control band. The appearance of this line indicates that the test kit is working just fine. The second line will only appear of the test kit has detected the presence of HCG in the urine sample.

HCG or Human Chorionic Gonadotropin is one of the early hormones that appear when a woman is pregnant. This is released by the chorion, one of the fetal membranes that ensure the survival of the embryo.

Most often, the second test line appears as a dark, very visible line. This indicates that the urine does have HCG and it has reacted to the reagent in the test strip. This line appears when HCG in the urine binds and reacts with the antibodies in the test strip. As the urine sample runs through the antibody strip, any HCG present will be caught, react and cause the dye to become visible.

At times, the second line appears as a faint line. Most kits will consider this as still a positive pregnancy indicator. That is, as long as the faint line is read within the recommended clinical reaction time (i.e., within 5 minutes). However, it is still strongly advised to take the test again after 1 to 2 days to get a more definitive result. Use the first urine in the morning right after getting up from bed. Seeking medical consultation for further tests to confirm pregnancy or not is also strongly advised.

General Instructions

It is important that a home test be performed properly to get the most accurate results. The instructions slightly differ among the various brands and types of home test kits. In general, these are the guidelines when testing for pregnancy using home pregnancy test kits:

  • Use only test kits that have not yet expired. The chemicals in kits beyond the expiration date will no longer reliably work.
  • Test kits must be stored properly prior to use. Exposure of the kits to direct sunlight and other degrading factors can cause the chemicals inside to be unstable and unreliable.
  • Carefully read the instructions that come with the test kit. Manufacturers may have slightly different methods of doing the test. These differences may include the reaction time. Some manufacturers will require readings be made within 5 minutes. Others may require longer, waiting for as long as 10 minutes before readings can be made.
  • Read if the test kit requires special preparations before a urine sample is obtained. For example, some test kits may also be sensitive to certain food components or to changes in the body related to physical activity. Follow directions carefully to get the most accurate results.
  • Use a clock if the test kit requires specific timing. Guessing the time will only yield inaccurate results.

Evap line pregnancy test vs faint test line
Again, faint test line is widely considered as a positive pregnancy result. Evap lines are not. This table shows a summary of the main distinguishing features between an evap line and a positive pregnancy line.

Using and Interpreting the Home Pregnancy Test Kit and Evap line pregnancy test vs faint test line
Using and Interpreting the Home Pregnancy Test Kit and Evap line pregnancy test vs faint test line | Source
Faint Positive Line
Evap Line
Same thickness as the control (first) line
Often thinner than the thickness of the control line
Time of appearance
Within the recommended reaction time (depends on manufacturer's recommendation; typically 5 minutes, usually ranging from 3 to 10 minutes)
Usually beyond the recommended reaction time
Same color as the control line
Usually colorless, greyish, almost imperceptible

Faint test lines usually result from the following:

Taking the Test Too Early: Some women use a home pregnancy test even before a missed period. The best time to test is at least 7 to 10 days after the ovulation period. Earlier than that can result in a false negative or a faint positive reading. For a faint positive line, repeat the test after a few days. Use the first voided urine in the morning for this test. This urine sample is concentrated, which will likely have a higher concentration of HCG. This will give a more definitive result.

Test Sensitivity is Low: Test sensitivity varies among the many different brands of home pregnancy test kits. Check for the sensitivity level and choose a higher one to repeat the test. The faint positive line is more likely because the test kit used has a lower sensitivity to the woman’s urine sample components. Getting a test kit with higher sensitivity will give a more accurate result.

Check that the sensitivity of the test kit is appropriate for the stage in the suspected pregnancy. Typically, higher sensitivities are recommended for testing during the early stagesof pregnancy. These test kits use a different formulation in the antibody strip so that no matter how low the concentrations of HCG are, the antibodies will still pick it up. If using a lower sensitivity test kit (typically designed for testing during later stages, e.g., at 2 months of gestation onwards), low HCG levels during the first few days of pregnancy will not be detected. This can result in a faint test line.

Urine Sample is Diluted: It might be that the urine sample used is diluted. The concentrations of compounds in urine are too low, resulting in a weak reaction with the test strip.

Urine dilution happens for several reasons. Frequent urination is one cause of diluted urine. This gives urine very little time to become concentrated in the urinary bladder, resulting in a diluted sample.

Another common reason for diluted urine is large consumption of liquids a few moments before taking a urine sample.

To avoid using a diluted urine sample and get faint positive lines, the recommendation is to use the first urine in the morning. Generally, a home pregnancy test kit can be used at any time of the day, using urine from any time of the day. The first urine in the morning is more concentrated than any urine taken during any other time of the day. This is because urine has stayed in the urinary bladder for an entire night’s sleep. This period gave urine time to get more concentrated. For a pregnant woman, this urine will contain the highest concertation of HCG. Hence, the first urine in the morning is the best sample to use to get more accurate results.

Chemical Pregnancy: This is a condition wherein the fertilized egg miscarries before other signs of pregnancy can be detected. In this condition, the fertilized egg gets implanted into the wall of the uterus.

Implantation results in the release of HCG. This is relatively low in concentration compared to HCG during the rest of the pregnancy period.

During very early miscarriage, the fertilized egg gets implanted. It then detaches (miscarriages) before the fetal membranes (i.e., chorion, etc.) forms. If the fetal membranes fail to form, HCG levels will remain low.

Therefore, if the woman tests with a faint line, it might be that HCG levels were too low because of early miscarriage. HCG is still present in the blood and urine but the fertilized egg has already detached from the uterine wall. HCG presence gives the positive test result for pregnancy, but there is no longer any developing embryo. Hence, this is called chemical pregnancy.

The best next step is to repeat the pregnancy test. HCG levels in the body typically double every 48 hours. As the levels of HCG rise, the positive test line should grow darker.

Better yet, consult a qualified medical expert for confirmatory tests, i.e., an ultrasound. Seeking the aid of a medical expert for further tests is the better option. There are instances when false positive results happen with home pregnancy test kits. HCG levels are affected by several factors and are not limited to the presence of a fetus in the womb.

In addition, a faint positive result may be obtained and then a menstrual period occurs. This may not even be a false positive. Rather, this may be an early miscarriage. This is why checking with a medical practitioner is better when a faint positive line is obtained. Again, the faint positive line must appear within the reaction time to qualify and not be treated as an evap line pregnancy test.

What To Do With Evap Lines

Evap line pregnancy test means nothing so it has to be discarded. It does not indicate pregnancy and is merely a result of evaporation. Do not make the mistake of considering this as a faint positive line.

There are a few instances when the evap line pregnancy test appears within the reaction period. This is most likely not an evap line. Within 5 minutes, urine will still be saturating the test strip and would not have started to evaporate. Hence, it is more likely a faint positive result and not an evap line. It is considered as a positive line no matter how faint it appears to be, as long as the line appeared within 5 minutes.

Other Characteristics of An Evap Line
On blue dye tests, evap lines are also very faint. This type of pregnancy test kit has two windows. One elongated window will show the control line, indicating that the test kit is working well. Right beside this is another round window, where the test lines will show up. A single horizontal line appears for a negative pregnancy test. If positive for pregnancy, there will be one horizontal line intersected by one vertical line, forming a plus sign. The evap line typically shows up as a very faint, thin and almost colorless vertical line. The horizontal line always turns out dark blue and solid. The vertical line varies, depending if pregnancy is present or how concentrated the HCG in urine is. In addition, the vertical line may turn out to be an evap line.

Evap line pregnancy test is generally colorless, but not always. There are some evap lines that do have color. The color, however, is very faint and not as dark as the color of the control line.

Indented Lines: There are a few cases where the line appears in a place other than where it should be. For instance, the line should appear at the center of the test window. If the line shows up anywhere but at the center (or not evenly spaced with the control line), this is called an indented line.

Indent lines are completely colorless. These can appear as a white line in some cases. These can show up within the frame or outside.

This kind of line is fairly common and can also be misinterpreted as a positive pregnancy indicator. Indent lines are simply the antibody strip of the test kit. It isn’t anevap line, pregnancy testpositive test result or even a false positive one. However, if the indent line is grey or with color (however faint), then it is considered as an evap line.

Dye Runs: Dye runs are smudged lines in the area where a true test line should show up. This is a false line. A true test line should be solid, not a smudge.

This is considered a false line. Dye runs are usually a result of the dye not being able to run smoothly across the test strip. It can get stuck and accumulate in one area of the strip.

A dye run may look like a promising indication of a positive pregnancy, it isn’t. This is also not an evap line.

When this happens, this means that the test results are unreliable. It does not indicate either a negative or a positive pregnancy test. The next best step is to repeat the test.

Disappearing Line: This is another famous confusing line in the home pregnancy testing arena. The disappearing line is a positive line that disappears after a few minutes or hours. This is a huge downer for those who have celebrated with the positive result only to be confused when it disappears.

A disappearing line is not considered as an evap line. Pregnancy testresult is not reliable in this case. This happens when the entire dye has not finished flowing over the entire test strip. The dye can briefly get stuck in the right spot and then continue moving along.

True Positive Test Result: A true, reliable positive result is when the test line is solid, colored and does not go away. The color should be the same as the control line. The width should also be the same. It should be very visible and remains to be so even after 48 hours. The positive test line in most brands will never go away.

What differentiates an evap line from other lines appearing on the test kit?

  • Colorless or very faintly colored
  • Solid colored line
  • Completely colorless
  • Smudged colors
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