Accuracy of PSA Tests

Many Factors Elevate and Lower PSA Results
From sex the night before to taking aspirins and advancing age, the PSA test is sensitive to a host of influences. Most men facing a PSA (prostate-specific antigen) test for prostate cancer may not realize that many factors can influence the result. Nor do doctors always provide patients with a list of things not to do or not to take before the test. So here's a partial list of things that affect a diagnostic PSA test, both up and down.

What Elevates the PSA Test
The higher a man's PSA level, the more likely it is that cancer is present. Here are some factors that elevate a result:

  • Age alone can increase PSA levels. The older a man gets, the likelier his PSA will rise, yet it may mean nothing. For instance, a man might have a PSA reading of 5.5 at seventy, and not have cancer; yet that score in a fifty-something would raise concern.
  • Sex. Doctors generally recommend men should abstain from sex at least two days prior to testing. Studies show that ejaculation within that period before a PSA test may increase PSA levels in the blood.
  • Stimulation of the prostate, such as a prostate massage or a long bike ride, could elevate PSA levels.
  • Inflammation of the prostate gland. Prostate problems, such as benign prostatic hyperplasia (BPH) or prostatitis, can inflate PSA levels.
  • Infections of the prostate may cause PSA levels to rise. These can produce no symptoms, so patients might not be aware of them.
  • A man with a larger than average prostate may have a higher than normal PSA reading, even if this prostate is healthy. (A larger prostate produces more PSA into the blood.)
  • Digital rectal exams and biopsies of the prostate may cause PSA levels to rise. It should be noted that an increase in PSA caused by a DRE is not thought to be significant enough to produce a false-positive result. On the other hand, a biopsy may elevate PSA levels for as long as four weeks.

What Lowers PSA Test Results
Other factors can artificially lower the PSA level:

  • Certain medications used to control urinary problems from BPH and prostatitis -- such as finasteride or dustasteride, which are prescription medications, or saw palmetto, an over-the-counter herbal remedy - can lower PSA levels by as much as 50 percent.
  • New research shows that men who use common painkillers such as non-steroidal anti-inflammatory drugs (NSAIDs) and aspirin on a regular basis had PSA levels that were about 10 percent lower than the men who did not use them. (HealthNews, Sept 11, 2008)
  • A lowering effect was seen for regular use of acetaminophen (Tylenol), although it did not reach statistical significance. (HealthDay, September 8, 2008).

What's a Normal PSA Level?
Unfortunately for men, 'normal' seems to be a bit of a moving target. Because of various factors such as age and medications, PSA levels tend to fluctuate. One abnormal PSA test can be quite meaningless.

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