An invalid pregnancy test occurs when the patient does not see any visible line in the pregnancy test kit after completing the test, according to Early-Pregnancy-Tests.com. The result is neither positive nor negative, and another test needs to be conducted.
Early-Pregnancy-Tests.com explains that insufficient amount of urine sample or not following the test procedure correctly are possible reasons for invalid results. Pregnancy test kits contain detailed test instructions that the patient needs to follow in order to obtain an accurate result. If there is too little or too much urine or even slight mishandling of the test, it can result in an invalid test.