Probability of prostate cancer as a function of the percentage of free prostate-specific antigen in patients with a non-suspicious rectal examination and total prostate-specific antigen of 4-10 ng/ml.

Our aim was to assess the usefulness of measuring the percentage of free prostate specific antigen (PSA) in serum in relation to reducing the number of prostate biopsies in men with benign prostate examinations and serum PSA levels between 4 and 10 ng/ml. The percentage of free PSA (Immulite) in serum was analyzed prospectively in 500 men, all of whom underwent ultrasound-guided sextant prostate biopsies. Cancer was detected in 21.4% (107/500) of the patients. Using a free PSA cutoff of < or = 23% as a criterion for performing prostate biopsy would have detected 94.4% of cancers, avoided 18.8% of benign biopsies and yielded a positive predictive value of 25.3%. The percentage of free PSA increased with prostate volume. Mean total PSA and mean free percent PSA values increased as patient age increased, influencing the calculation of cutoff values, sensitivity and specificity. PSA density had a sensitivity and specificity not significantly different than the percentage of free PSA. Measurement of the percentage of free serum PSA improves the specificity of prostate cancer detection in patients with elevated total serum PSA levels and benign prostate examinations.