PSAProstate specific antigen

Prostate specific antigen is a protein produced by the prostate gland whose normal job is to liquefy semen. A small amount leaks into the blood, and more does so when the prostate is enlarged, inflamed or diseased.

It matters because it is the standard prostate screening blood test, and because it is not specific to cancer. Benign enlargement, infection, recent ejaculation, cycling and a recent examination all raise it, so a raised value prompts further assessment rather than a conclusion.

In practice results are read against age, alongside examination and, where indicated, imaging. The balance of benefit and harm in population screening remains genuinely debated.