Definition - What does Evaporation Line mean?
An evaporation line is a colorless line that shows up in the result window of a home pregnancy test (HPT) due to the evaporation of urine. The appearance of this line doesn’t indicate pregnancy.
FertilitySmarts explains Evaporation Line
It's not unusual for evaporation lines to appear on the home pregnancy tests that use lines to indicate or refute a pregnancy. This line can show up due to a delay in reading the results within the given time window, or an error in the technique of the test — both of which cause the urine to evaporate and leave a confusing, colorless line behind.
The chances of getting an evaporation line are also higher if the pregnancy test is done too early. This is because the HPT looks for a specific hormone called human chorionic gonadotropin (hCG) in urine, the levels of which are low soon after conception and may not be detectable by the standard sticks.
The errors that result in an evaporation line can be overcome by using newer digital pregnancy tests, where the result shows up in words as “Pregnant” or “Not pregnant,” thus avoiding the confusion that springs from the lines of non-digital tests. Also, since hCG may not be detectable early on, but ramps up every other day if a woman is pregnant, waiting for a few days and then re-testing will also help yield a clear (positive or negative) result.