Prostate specific antigen is an enzyme that helps keep semen in its liquid form.
Prostate Cancer Canada - PSA
Prostate specific antigen (PSA) is protein 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 found in the blood, while cancer produces more of the attached form.
A PSA blood test measures the amount of PSA found in the blood. PSA levels in the blood increase when the size of the prostate, or the number of prostate cells, increases. The PSA test combined with the digital rectal exam is the most accurate guide to early cancer detection.
The PSA level that is considered normal for an average man ranges from 0 to 4 nanograms per millilitre (ng/ml).