Prostate specific antigen (PSA) is a protein in men that is secreted into ejaculate fluid by the healthy prostate. One of its functions is to aid sperm movement. Normally, only very low levels of PSA are able to enter the bloodstream. However, several conditions of the prostate can cause the PSA levels in the blood to rise. These include benign prostate enlargement, infection of the prostate and prostate cancer.
Benign enlargement of the prostate due to a condition called benign prostatic hyperplasia (BPH) occurs in older men and often causes urinary symptoms such as slow urine flow or stopping and starting urination. Because there are more prostate cells to produce PSA, the levels rise and this increases with age. For this reason, age-based thresholds (Table 1) can be used to decide if a test result is abnormal. The percentage free to total PSA ratio (described below) also helps to show whether raised PSA is due to benign enlargement. Benign enlargement does not ‘turn into’ prostate cancer.
A temporary rise in the PSA can be caused by a number of conditions: urinary infection, prostatitis (inflammation of the prostate) or a biopsy of the prostate. They can cause large rises. Small rises can be caused by ejaculation and even bicycle riding. Because of these non-cancer causes of PSA rises, it is not surprising that if you have an abnormally high test result, it is not always due to prostate cancer. The chance that you have prostate cancer given an abnormal PSA result is only about 1 in 3. If, in addition to the PSA test, you have a digital rectal examination, and it also is abnormal, your chances of having prostate cancer are greater (1 in 2).