This is because PSA is a protein made and secreted by the prostate gland into the semen. The PSA blood test actually measures the level of ‘leak’ of this protein into the blood stream. Therefore, the larger the prostate gland, the larger the leak.

Any process that upsets the normal barriers between the prostate gland ducts and the blood stream will increase this ‘leak’, thus raising the blood value of PSA. These processes include cancerous change andinflammatory ones too e.g. prostatitis (Link to PDF).

Nevertheless, a high PSA reading does require further investigation in most cases; this is usually in the form of a Trans-rectal ultrasound and prostate biopsy.

For men who already have a diagnosis of prostate cancer, PSA is usually a very effective tool in monitoring either progression or otherwise of the disease or indeed response to treatment thanks to its high specificity.