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Enlarged Prostate Special Report

What Does It Mean? PSA Terminology Explained

The American Urological Association recommends an annual PSA (prostate-specific antigen) test to screen them for prostate cancer beginning at age 50. Recently, researchers have developed several ways to improve the PSA test’s accuracy. In this Health Alert, Johns Hopkins experts explain PSA density, PSA velocity, and other PSA measurements.

PSA is an enzyme produced almost exclusively by the glandular cells of the prostate and normally only very small amounts of PSA are present in the blood. High levels of PSA can indicate prostate problems, including BPH and prostate cancer. But high PSA levels can also be caused by a variety of daily activities.

To improve the accuracy of the PSA test researchers now assess PSA levels in relation to prostate size (PSA density); monitor annual changes in PSA velocity; measure the ratio of free to total PSA (percent free PSA or complexed PSA); and adjust the PSA result for a patient’s age (age-specific PSA).

Here is a brief explanation of these important PSA measurements.

  • PSA density -- assessing PSA level in relation to prostate size
    PSA density takes the size of a man’s prostate into account when evaluating his PSA level. It is calculated by dividing the PSA value by the size of the prostate (as determined by transrectal ultrasound). This measurement helps doctors distinguish between BPH and prostate cancer: The higher the PSA density, the greater the chance of cancer, because the elevated PSA level is less likely to be the result of daily activities or benign prostate enlargement.
  • PSA velocity -- monitoring annual changes in PSA velocity
    This measurement takes into account annual changes in PSA values, which rise more rapidly in men with prostate cancer than in men without the disease. PSA velocity is especially helpful in detecting early cancer in men with mildly elevated PSA levels and a normal digital rectal exam.
  • Percent PSA -- measuring the ratio of free to total PSA (percent free PSA or complexed PSA)
    PSA in the blood is either bound (attached to proteins) or unbound (free). PSA assays usually measure the total PSA (both free and complexed). Other assays measure the percentage of free PSA or the percentage of complexed PSA.
  • Compared to men with BPH, men with prostate cancer have a higher percentage of bound PSA and a lower percentage of free PSA. Research suggests that determining the ratio of free to total PSA in the blood helps distinguish between PSA elevations due to cancer and those caused by BPH.

  • Age-specific PSA -- adjusting the PSA result for a patient’s age
    PSA increases with age because the prostate gradually enlarges as men grow older. Some years ago, researchers suggested adjusting PSA levels to the age of the patient: Higher levels would be considered normal in older men, and lower levels considered normal in younger men. However, there is concern that the use of higher PSA thresholds in older men will miss important cancers.

Posted in Enlarged Prostate on January 17, 2009

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