PSA (prostate specific antigen) is a chemical produced by the prostate gland. It functions to liquefy semen following ejaculation, aiding the transit of sperm to the egg. A small amount of PSA filtrates from the prostate into the blood circulation and can be measured by a simple blood test. In general, the larger the prostate size, the higher the PSA level since larger prostates produce more. As a man ages, his PSA rises based upon the typical enlarging prostate that occurs with growing older.

Although it’s an imperfect screening test, PSA remains the best tool currently available for detecting prostate cancer. It shouldn’t be thought of as a stand-alone test, but rather as part of a comprehensive approach to early prostate cancer detection. Baseline PSA testing for men in their 40s is useful for predicting the future potential for prostate cancer.

Upon PSA testing, about 90% of men are found to have a normal PSA. Of the 10% of men with an elevated PSA, 30% or so will have prostate cancer. In a recent study of 350,000 men with an average age of 55, median PSA was 1.0. Those with a PSA < 1.5 had a 0.5% risk of developing prostate cancer, those between 1.5-4.0 had about an 8% risk, and those > 4.0 had greater than a 10% risk.

PSA screening is imperfect because of false negatives (presence of prostate cancer in men with low PSA) and false positives (absence of prostate cancer in men with high PSA). Despite its limitations, PSA testing has substantially reduced both the incidence of metastatic disease and the death rate from prostate cancer.

Men age 40 and older who have a life expectancy of 10 years or greater are excellent candidates for PSA screening. Most urologists do not believe in screening or treating men who have a life expectancy of less than 10 years. This is because prostate cancer rarely causes death in the first decade after diagnosis and other competing medical issues often will do so before the prostate cancer has a chance to. Prostate cancer is generally a slow-growing process and early detection and treatment is directed at extending life well beyond the decade following diagnosis.

Prostate biopsy (ultrasound guided) is the definitive and conclusive test for prostate cancer. An elevated or accelerated PSA, abnormal digital rectal exam and suspicious MRI are all helpful.