Prostate-specific antigen (PSA) blood test

Prostate-specific antigen (PSA) is a substance produced by the prostate gland. Elevated PSA levels may indicate prostate cancer or a non-cancerous condition such as prostatitis or an enlarged prostate.

PSA levels are measured in nanograms per millilitre of blood (ng/ml). Whether a PSA level is “normal” depends on the individual and their age. Cancer Research UK uses the following rough guide:

• 3 ng/ml or lower is considered in the normal range for a man under 60 years old
• 4 ng/ml or lower is normal for a man between 60 to 69 years old
• 5 ng/ml or lower is normal for a man 70 years old and over

A reading higher than 5ng/ml but lower than 10 ng/ml is usually due to a benign enlarged prostate, Cancer Research UK says. A reading above 10 ng/ml may also indicate benign prostate disease. However the higher the PSA level, the more likely it is to be prostate cancer.

Most men have PSA levels under 4 ng/ml, and traditionally this has been used as the cut-off point for concern about the risk of prostate cancer. Men with prostate cancer often have PSA levels higher than four, although cancer is a possibility at any PSA level. According to published reports, men who have a prostate gland that feels normal on examination and a PSA level below 4 ng/ml have a 15% chance of having prostate cancer. Those with a PSA level between four and 10 have a 25% chance of having prostate cancer and if the PSA is higher than 10, the risk increases to 67%.

Due to findings from more recent studies, some experts now recommend lowering the cut-off point that determines whether a PSA value is normal or elevated. Some researchers favour below 2.5ng/ml or 3 ng/ml as a cut-off for normal values, particularly in younger patients. Younger men tend to have smaller prostates and lower PSA values, so any elevation of PSA levels above 2.5ng/ml in this population may be cause for concern.

The NHS has a referral threshold of 3 ng/ml for men between 50 and 59 years old; 4 ng/ml for men between 60 and 69 years old, and 5 ng/ml for men 70 years old and over.

Just as significant as the PSA level is the trend in that number (whether it is going up, how quickly and over what period of time). It is also important to understand that the PSA test is not infallible. Most men with elevated PSA levels have non-cancerous prostate enlargement, which is a normal part of ageing. Conversely low levels of PSA in the bloodstream do not rule out the possibility of prostate cancer. However most cases of early prostate cancer are found by a PSA blood test.