Prostate-specific antigen (PSA) is an enzyme produced exclusively by the prostate gland. It helps to liquify the semen. Most men have PSA levels < 4 ng/dL and this has traditionally been used as the cutoff for prostate disease. Elevated PSA levels may indicate prostate cancer or noncancerous conditions such as prostatitis or enlarged benign prostate.
PSA testing is generally done in men above the age of 50 years. To include it in health screening in healthy men below this age is not recommended as it can lead to undue anxiety if it is found to be raised. Indeed, the level can continue to be elevated even on repeat testing. One postulate for elevated PSA values in asymptomatic young men is that they have ‘leaky’ prostates which allow more PSA to escape into the bloodstream. Some doctors attempt to treat high PSA levels with antibiotics on the assumption that there is some underlying prostate infection. If so, the antibiotics ought to be given for a month and PSA re-tested 3 months later to allow for sufficient time for the infection to clear and level to drop. In men who have benign prostate enlargement (BPH), testosterone- inhibitor drugs like finasteride (Proscar) or dutasteride (Avodart) can artificially reduce the PSA value by half. Hence, the actual PSA value is double that of what is reported. If the fall in PSA is not as expected when men with BPH have been given such drugs, then underlying prostate cancer has to be excluded.
Men with prostate cancer often have PSA levels > 4 ng/dL, although cancer is also possible at PSA levels below that. According to published reports, men who have a prostate gland that feels normal on examination and a PSA less than four have a 15% chance of having prostate cancer. Those with a PSA between 4 and 10 have a 25% chance of having prostate cancer and if the PSA is higher than 10, the risk increases to 67%. Some recent studies recommend lowering the cutoff levels to less than 2.5 or 3 ng/dL for young men who have a family history of prostate cancer. To further predict the likelihood of cancer, the free/total PSA ratio is also available. The lower the percentage (eg < 10%), the higher the chance of cancer. However, this reading only applies to PSA levels between 4 to 10 ng/dL and assumes that there is no underlying prostatitis. Even then, it has not been validated in Asian men.
Just as important as the PSA reading is the PSA kinetics, eg. whether it is going up, how quickly, and over what period of time. It is important to understand that the PSA test is not perfect. Most men with elevated PSA levels do not have prostate cancer. The best way to confirm the cause of high or rising PSA value is to do prostatic biopsies [Fig 1]. This is easily done in the clinic under local anaesthesia and antibiotic cover. Upon confirmation of cancer, the PSA then becomes a useful marker to monitor response to treatment.