Prostate-specific antigen (PSA) is the most important serum tumor marker for prostate cancer detection. Free PSA is one of the many molecular forms of PSA that have been identified. Percent free PSA improves the specificity (elimination of unnecessary biopsies) for prostate cancer detection in men with nonsuspicious digital prostate examination and total serum PSA ranges between 4 and 10 ng/mL. Further study is necessary to determine the optimal clinical utility of percent free PSA in men with a total serum PSA level of less than 4 ng/mL. In addition, the level of free PSA may be affected by many factors, including age, prostate volume, prostate manipulation, sample handling, and type of assay used.
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