What are Pregnancy Test Evaporation Lines?

Evaporation lines are caused by evaporation of the urine in the result window of a pregnancy test. These are lines that shows in the result window of the test. An evaporation line develops when the urine on the test area begins to dry, leaving a faint, colorless line. Evaporation lines appear as a result of the composition of the particular urine specimen – and they may appear on any test regardless of brand.Evaporation lines can confound results if tests are not interpreted within the clinically recommended time frame. The complete reaction time of our pregnancy tests is 5 minutes. With most home pregnancy testing products, the “reaction time” of the test is a minimum five minute interval to verify a negative result for pregnancy. Generally, at three to five minutes, you can interpret the test results. To be accurate, the test results should be read within the reaction time of the test, which is usually at 5 or so. Manufacturers also recommend that you should not read tests after a designated time period, as most test brands have the possibility of developing evaporation lines.

Once the reaction time of the home pregnancy test is complete, color bands will either appear or not appear in the test region of the strip or midstream unit. All tests have a “control” color band or color line that indicates whether the test is working or not. The “test” color band indicates a positive or negative result.

Assuming that the home pregnancy testing procedure has been followed properly and the results have been interpreted within the time frame indicated by the manufacturer, a faint line in the test region of the result window may be read as a positive result, though it’s a good idea to verify the result in a day or two using a first morning urine sample.

Now, an evaporation line will not be confused with a faint test line (valid positive) if the test is read within the five minute reaction time interval. Other explanations for faint test lines include:

Testing Too Early in Your Cycle: If you test too early, earlier than seven to ten days past ovulation, the hCG may not be at a sufficient level to produce more than a very faint line. If you do see a faint positive test result, then we always recommend a follow up test in a day or two using that first morning urine.

Lower Test Sensitivity: Different tests have different sensitivity levels. Check the sensitivity level of your test and try to purchase higher sensitivity pregnancy tests so you can have accurate results sooner.

Diluted Urine Sample: Urine samples may experience “dilution” due to frequent urination or consumption of liquids. This is whey first morning urine is recommended for pregnancy testing as it contains the most concentrated amount of the hormone, hCG.

Chemical pregnancy: A chemical pregnancy is indicated when implantation of a fertilized egg takes place and hCG is produced. A chemical pregnancy is, by definition, very shortly followed by miscarriage before any other pregnancy signs can be detected. Hence, a faint positive line on a pregnancy test may be detected, but there is a a miscarriage very quickly following implantation.

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