Medical Edge Newspaper Column

PSA Test Alone Not Enough to Diagnose Specific Condition

January 20, 2012
Dear Mayo Clinic:
What do you recommend as far as PSA testing? Is it true that the test is not completely accurate?

Answer:
The prostate-specific antigen (PSA) blood test can be a valuable tool for detecting prostate problems, particularly prostate cancer. But a PSA test alone is not enough to diagnose a specific condition. To be most useful, PSA results need to be considered within the context of a man's health history and current medical situation.

The PSA test is a simple blood test developed in the late 1980s. PSA is a protein that the prostate — a gland that sits below a man's bladder — releases into the bloodstream. PSA is mostly found in semen. Small amounts of PSA in the blood are normal.

The amount of PSA in blood can rise to abnormal levels for a variety of reasons, including a common condition called benign prostate enlargement, also known as benign prostatic hypertrophy or hyperplasia and abbreviated BPH. An infection within the prostate can also increase the PSA. The most significant cause of elevated PSA is prostate cancer. Cancer can change the structure of the prostate, allowing excess PSA to leak into the blood.

The PSA test is often used to screen men for prostate cancer. A PSA number that is higher than normal could signal the need for a prostate biopsy. That procedure involves taking a sample of prostate tissue and evaluating it for cancer. But one PSA test result alone is usually not enough for a doctor to make an informed decision about whether to recommend a biopsy.

For example, a digital rectal exam can also be used to evaluate the prostate and look for signs of cancer. A doctor performs the test by inserting a lubricated, gloved finger into the rectum to feel the prostate for bumps or other abnormalities. A digital rectal exam should always be done in conjunction with a PSA test when screening for prostate cancer, as it helps reduce the risk of missing a tumor.

Risk factors such as age, race, and family history also should be considered. As men age, the risk of prostate cancer rises. Most prostate cancers are found in men 65 and older. Men of African-American descent also are at higher risk. In addition, men who have a family history of prostate cancer are at increased risk, particularly those who have a father or brother who was diagnosed with the disease.

The opportunity to compare PSA test results over time is helpful for doctors. For that reason, getting a PSA test when a man is in his early 40s can be valuable. Using that result as a baseline can help determine when future PSA tests should be done, as well as show how much change has taken place and how quickly the PSA has risen.

Many health organizations have issued guidelines for PSA testing. Most urologists believe discussions about whether to have a PSA test should begin when men are in their 40s.

While PSA testing can identify prostate cancer at a stage when it can be cured the test has disadvantages, and the results can be difficult to interpret. The bottom line is that PSA testing should occur as part of a conversation between a man and his doctor. Men need to understand the pros and cons of PSA for their individual situation. There is no one-size-fits-all approach for PSA testing.

— R. Jeffrey Karnes, M.D., Urology, Mayo Clinic, Rochester, Minn.