Prostate specific antigen (PSA) is a natural chemical produced by the prostate gland. Any condition that irritates or damages the prostate gland can lead to a leakage of PSA into the blood. PSA is a way of identifying abnormalities of the prostate, but it is not specific to prostate cancer alone.
Reasons for an elevated PSA include:
- benign prostatic hypertrophy (BPH)
- prostatitis
- prostate cancer
- recent prostate biopsies
- bladder surgery
- prostate surgery
- prostatic massage
- recent ejaculation
- anything that manipulates the prostate (e.g. riding a bicycle).
Normal levels of PSA range between 0–5 ng/ml. However this differs according to the man’s age and also to the size of the prostate. It has been standard practice for men who are found to have an abnormal PSA level to have a prostate biopsy, because they are considered at risk of prostate cancer. However, recent data from the Prostate Cancer Prevention Trial (PCPT), have demonstrated that prostate cancer is also a common finding on biopsy in men with a normal PSA level. Within the range 1–10ng/ml, the PSA level is not a good guide as to which men have prostate cancer and which do not.
PSA can be found in the blood in different molecular forms. It may be 'free' or 'bound' to other proteins. Men with benign prostatic hyperplasia (BPH) have more of the free form. Men with prostate cancer have more of the bound form. It is suggested that determining the 'percent free PSA' (the ratio of free to total PSA) might help to distinguish between prostate cancer and BPH.
In men who have already been diagnosed with prostate cancer, PSA is invaluable as a 'tumour marker' to assess response to therapy and monitor the progress of disease.