Health problems, especially those that affect the endocrine system (which is responsible for hormones), can also cause false positive tests. Kidney disease, which results in blood and protein in the urine, has the same effect - pregnancy tests often confuse protein in the urine with hCG. In rare cases, a false positive test may indicate that a woman has uterine cancer. In general, if you've ruled out pregnancy and the test still comes out positive, you might want to see a doctor.