PSA stands for prostate specific antigen. The prostate is the only place in the male body where this "hormone" is made. Women, therefore, do not have any PSA detectable in the blood. The prostate is a walnut-sized gland that sits below the bladder and surrounds the urethra. It contributes about 50 percent of the ejaculate volume, which helps the sperm survive for reproduction. PSA has a role itself in reproduction and also helps the sperm survive. The PSA is detectable in the blood through a special blood test.
The prostate can "leak" PSA into the bloodstream that we can then measure. There are several instances where the PSA may be elevated. As men age, the prostate tends to get bigger and therefore the prostate of an 80-year-old man will usually secrete more PSA than a man in his forties. An infected prostate will tend to "leak" more PSA and may cause the level to be falsely elevated. In this situation the man is usually treated with antibiotics and a PSA is redrawn at a different date. Another situation where the PSA can be elevated is prostate cancer. A rectal examination should also be performed to identify any abnormalities. A prostate biopsy is often necessary to differentiate these three situations and rule out prostate cancer.
The normal PSA value is usually stated to be less than 4.0. However, because of the fact that benign enlargement of the prostate gland tends to occur as men get older, an age-adjusted scale has been developed:
- 0-2.5: Normal for a man 40-50 yrs.
- 2.5-3.5: Normal for a man 50-60 yrs.
- 3.5-4.5: Normal for a man 60-70 yrs.
- 4.5-5.5: Normal for a man 70-80 yrs.
The PSA is not a perfect test but it can aid in detecting prostate cancer. Other factors that may falsely elevate the PSA value include a prostate biopsy, cystoscopy, vigorous rectal examination and ejaculating 48 hours before the sample is drawn. A new PSA test has been developed to better distinguish whether the PSA is elevated from prostate cancer or benign prostate disease and is called a free PSA. This test is based upon the fact that some of the PSA in the blood is bound to proteins, while some freely circulates in the blood. The lower the percentage of free to total PSA (<15 percent), the greater the worry that an individual has prostate cancer. Newer, more sensitive PSA tests are on the horizon and may help us in detecting prostate cancer more efficiently in the future.
The American Cancer Society recommends that men over 50 years of age should have an annual rectal examination and PSA. Individuals of African-American descent or those with a family history of prostate cancer should begin screening at age 40.