What is the role of free prostate-specific antigen (PSA) measurement in prostate screening?

Updated: Jan 14, 2019
  • Author: Lanna Cheuck, DO; Chief Editor: Edward David Kim, MD, FACS  more...
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The measurement of bound and free PSA can help to differentiate mildly elevated PSA levels caused by cancer from elevated levels resulting from benign prostatic hyperplasia. The lower the ratio of free-to-total PSA, the higher the likelihood of cancer. (Free PSA is reported as a percentage.) For example, among men with greater than 25% free PSA, only 8% are found to have cancer at prostate biopsy.

In contrast, more than half of men with less than 10% free PSA are found to have cancer at biopsy. While cutoffs may be used, the percentage of free PSA is usually employed as an additional factor in making an informed recommendation for or against biopsy. Generally, these percentages are useful in patients who have a PSA level in the range of 4-10ng/mL.

This information is most useful in men with very large glands or in whom 1 biopsy result has already been negative. In healthy men with a PSA level of 4-10ng/mL, many recommend biopsy without the additional free-PSA test or consider a trial of antibiotic therapy for 4-6 weeks before repeating the PSA test. (If antibiotic therapy quickly lowers the PSA level to within the reference range, the cause of the prior elevation is less likely to be prostate cancer, and the PSA test should be repeated within a few months.)

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