ABSTRACT
Background: The predictive value of prostate specific antigen for prostate cancer, when levels are between 4 and 10 ng/ml, is low. Within these range of values, some authors recommend the measurement of the free fraction of the antigen to improve its predictive capacity. Aim: To evaluate the predictive value of the free fraction in subjects with prostate specific antigen values between 4 and 10 ng/ml. Patients and methods: One hundred and forty subjects with prostate specific antigen between 4 and 10 ng/ml were evaluated. All were subjected to transrectal ultrasound examination with biopsies and the free fraction of the antigen was measured by enzyme immuno assay. Results: Cancer was diagnosed in 36 subjects, all others had a benign prostatic hyperplasia. Mean prostate specific antigen values were 7.4 and 7.1 ng/ml in patients with cancerand hyperplasia, respectively. The percentage of free prostatic specific antigen was 9.8 and 19.8 percent in subjects with cancer and hyperplasia respectively (p <0.001). Using receiver operating characteristic (ROC) curves, a free prostate specific antigen of 13 percent was the best cutoff value for predicting prostate cancer. Conclusions: In subjects with prostate specific values between 4 and 10 ng/ml, the measurement of the free fraction of this antigen can improve the predictive value of this parameter for the detection of prostate cancer