Evap Line Pregnancy Test: Results and Interpretation
What Does an Evaporation Line Mean on a Pregnancy Test?
It can be confusing when a woman sees two lines on her pregnancy test—one dark and another very faint. In most cases, a faint line indicates a positive pregnancy. However, a faint line could also be a result of urine that evaporates and dries out after the recommended reaction time period (approx. five minutes). An evaporation line is a very faint, colorless line that appears when urine in the test window evaporates and dries out. It is not an indication of hCG hormone reacting with the reagent in the home pregnancy test strip and does not indicate a positive pregnancy. Unlike a faint positive line, which can be a light blue or pink (depending on the brand of the test), an evaporation line is nearly colorless.
What Causes an Evaporation Line?
An evaporation line appears when a woman waits too long and reads the result after the recommended reaction time period (usually five minutes after testing). This is why it's important to read the results right way. Some women keep the test strip after seeing a negative result and then check on it again after the recommend time and assume they're pregnant when they see a faint line. If the test turns out negative within 5 minutes of testing, then it is negative. Waiting a few more minutes will not make it a positive result!
Evaporation lines do not always appear for every test. This is because urine has very unique characteristics and composition among different individuals. Some women may see an evaporation line after five minutes while for others, this line may appear in an hour or so.
Faint Line vs. Evaporation Line
Faint Positive Line
Same thickness as the control line
Often thinner than the thickness of the control line
Time of appearance
Within the recommended reaction time. (This depends on the brand's recommendation, but it is typically 5 minutes.)
Anytime beyond the recommended reaction time (usually after 5 minutes or more).
Same color as the control line
Usually colorless, greyish, almost undetectable
The Difference Between an Evaporation Line and a Faint Positive
If you see a faint line within the reaction time period, it is not an evaporation line. No matter how faint it is, this line is considered a positive and is an indication that you took the test too early—most likely right after implantation when hCG levels are still low—or your urine was diluted. An evaporation line appears after the allotted reaction time and is virtually colorless.
What Color Are Evaporation Lines on Pregnancy Tests?
Evaporation lines on pregnancy tests are generally colorless, but not always. There are some evaporation lines that do have color—either a light blue or light pink. The color, however, is very faint and not as dark as the color of the control line. The evaporation line can also sometimes appear greyish.
On blue dye tests, evaporation lines are 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. The horizontal line is always dark blue and solid. If positive for pregnancy, there will be one horizontal line intersected by one vertical line, forming a plus sign. The evaporation line typically shows up as a very faint, thin and almost colorless vertical line. If pregnant, the vertical line may be faint, which means there is a low concentration of hCG is in the urine, but if you read it after the recommended reaction time, the vertical line may turn out to be an evaporation 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.
An evaporation line does not indicate pregnancy and is merely a result of evaporation. Do not make the mistake of considering this as a faint positive line.
Using and Interpreting the Home Pregnancy Test Kit
Most home pregnancy testing kits require a minimum of five minutes of reaction time. This is the time needed in order for the chemicals in the test kit to react with the hCG hormone in a woman's urine.
There are two basic types of home pregnancy test kits:
- The most common ones are dipsticks or test strips, which you either dip in a cup of urine or hold under a stream of urine. The urine will saturate the test strip. If there is hCG present, it will react with antibodies in the antibody strip. Dye will accumulate in this area and a second line will appear, indicating a positive pregnancy. If no HCG is present, then there will be nothing on the antibody strip to react to the dye.
- The second type of home pregnancy test uses a test device and a urine collection cup. A urine sample is collected in the cup and the test device is placed in it. Another version of this test kit has a small well on one end where you place a few drop of urine in using a dropper. If pregnancy is detected, the test device changes color.
Home pregnancy tests nowadays are very reliable, provided you use a concentrated urine sample and do the process correctly. The best sample is the first urine in the morning. This will give the most accurate 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.
Do note that a negative or a positive result on a home pregnancy test kit is not a definitive result. So many other factors may produce false positive or false negative results. If you think you may be pregnant, always get a checkup with a medical practitioner for confirmation.
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.
Faint Test Lines 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 seven to 10 days after ovulation or at least three days after your missed period. Testing earlier than that can result in a false negative or a faint positive reading. If you get a faint positive line, repeat the test after a few days. Use the first urine in the morning. This urine sample is concentrated and will likely have a higher level of hCG, which will give a more accurate result.
Home Pregnancy Test Sensitivity Is Low
Test sensitivity varies from brand to brand. Getting a test kit with higher sensitivity will give a more accurate result. Most tests are 20–25 miU/ml. The lower the number, the more sensitive the test will be. Typically, higher sensitivities are recommended for testing during the early stages of pregnancy. These test kits use a different formulation in the antibody strip so that no matter how low the concentration of hCG is, the antibodies will still pick it up. If you use a lower sensitivity test kit that is designed for testing during the later stages of pregnancy, the test will not be able to detect the low amounts of hCG. 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.
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.