Home pregnancy tests are nearly 100% accurate, but that accuracy depends on various factors in the body and in the performance of the test. In the majority of cases, the false negative and false positive result on a pregnancy test are directly linked to human error.
Human error can cause both a false positive and false negative pregnancy test result. The most common human errors include not allowing enough urine to be absorbed onto the testing stick and reading the evaporation line as a positive test result. The evaporation line is a thin grey line that can occur on the test result stick when the urine passes over the testing window. If the home pregnancy test is read too late, the result could also appear to be positive rather than negative. False positives could also be the result of a chemical pregnancy or interference from an infertility drug containing hCG.
The false negative pregnancy test is much more common than a true false positive. Many women are excited to find out if they are pregnant and take the home pregnancy test too early for urine hCG detection. The miscalculation of the first day of the next menstrual cycle could also lead to a false negative pregnancy test result. Other common reasons why a pregnancy test could read false when the woman is truly pregnant include waiting too long to read the test and not enough urine absorbing into the testing stick. If the pregnancy test is outdated, the chemicals used to test for hCG in the urine may not work effectively.
The false negative and false positive pregnancy test result is most often due to human error. If a woman feels she is pregnant, or not pregnant, a blood pregnancy test can provide a more accurate result. The qualitative blood hCG test will come back positive or negative for hCG in the blood. A quantitative blood hCG test will come back with the total amount of hCG present in the blood.