Most of the time, CT scans are very accurate, though false negatives and false positives can happen. A 2018 study found that some false positives can occur. Researchers cited 13 false negatives out of 710 scans. The main reason for them was CT scan technique. Researchers in the same study also found 43 false positives in 710 CT scans for people who had blood in their urine or a history of bladder cancer. Some false positives were attributed to: a harmless enlarged prostate (in males), a naturally thickening bladder, changes to medical treatment, the presence of blood clots, and inflammation.