A PSA blood test is a fairly accurate screening test for prostate cancer. PSA is a protein made by cells in the prostate gland, found mostly in semen but a small amount is also found in blood. The chance of having prostate cancer goes up as the PSA level goes up, but there is no set cutoff point that can tell for sure if a man does or doesn’t have prostate cancer.
Most men without prostate cancer have PSA levels under 4 ng/mL of blood. When prostate cancer develops, the PSA level often goes above 4. Men with a PSA level between 4 and 10—often called the borderline range—have about a 1 in 4 chance of having prostate cancer. A PSA of more than 10 means the chance of having prostate cancer is over 50%. If your PSA level is high, you might need further tests to look for prostate cancer.