Prostate specific antigen (PSA) is a serine protease glycoprotein, which is predominantly produced in the prostate. Blood levels of PSA are a useful indicator of prostatic pathology, to evaluate men at risk of prostate cancer, and for assessment after treatment.
In normal healthy individuals, PSA is secreted into the seminal fluid in high concentrations to liquefy seminal gel and help increase sperm mobility. A small amount of PSA is also normally found in the blood as a result of leakage from the prostate gland. Elevated blood PSA levels are a sign of prostatic pathology, particularly prostate cancer; however additional testing (e.g. biopsy) is required for an accurate diagnosis.