What is PSA?

Prostate-specific antigen (PSA) is a chemical produced by prostate cells. It supports sperm by helping keep semen in a liquid state. Whilst normally secreted into the semen, PSA can backflow into the bloodstream and be measured using a blood test.

The PSA level may be raised for many reasons. These include:

Prostate cancer

Benign enlargement of the prostate

Infection in the urine

Inflammation of the prostate

Operations on the urinary tract, such as cystoscopy to look into the bladder

Recent intercourse and ejaculation

External pressure on the prostate, for example from a bicycle seat after a long ride

PSA levels can fluctuate over time and vary from person to person. A man with significant cancer may have a normal PSA and, in the same way, a man who does not have prostate cancer may have a raised PSA.

PSA “density” measures the PSA level relative to the volume of the prostate. It helps clarify the significance of an elevated PSA in a men with enlarged prostates. A PSA density of > 0.15 carries an increased risk of prostate cancer.

The “free/total PSA ratio” is another refinement that can help assess risk. Men with prostate cancer have a greater fraction of PSA that is bound to other proteins in the blood, meaning they have a lower “free” PSA level. Those with a free/total ratio < 0.1 have a 56% chance of having prostate cancer. Men with a ratio > 0.25 have only an 8% chance of harbouring the disease.