Prostate specific antigen (PSA) is an enzyme produced in the ducts of the prostate and absorbed into the bloodstream. Here it may become bound to two proteins: anti-chymotrypsin (ACT) and alpha macroglobulin (aMG) . The "PSA test" measures the level of free and bound PSA in the blood. With benign prostate conditions, there is more free PSA, while cancer produces more of the attached form.
PSA test results show the level of PSA detected in the blood. The PSA level that is considered normal for an average man ranges from 0 to 4 nanograms per milliliter (ng/ml). A PSA level of 4 to 10 ng/ml is considered slightly elevated; levels between 10 and 20 ng/ml are considered moderately elevated; and anything greater is considered highly elevated. But because various factors can cause PSA levels to fluctuate, one abnormal PSA test does not necessarily indicate that cancer is present.
Combined, the digital rectal exam (DRE) and the PSA test are the most accurate guide to early detection of prostate cancer. You may also have heard of the prostatic acid phosphatase (PAP) blood test. This test is rarely performed, as it is less accurate than the PSA test.
