A pregnancy test may leave a light mark when it dries, but this should not be used to determine if you are pregnant. A pregnancy test that dries and leaves a light mark may be caused by the deposition of crystals as the urine dries. Also, if the urine specimen is contaminated, the test may dry and leave a light mark. If your period is delayed and you want to use a pregnancy test to determine if you are pregnant, you should learn how to use it correctly, including observing the change in color of the test strip within the prescribed time. It is recommended that the test be observed within 5 minutes for accuracy, as too long or too short a period of time may result in false positives or false negatives. The most accurate way to determine pregnancy is to take a blood test for HCG at the hospital or to have a vaginal ultrasound after 10 days of delayed menstruation.