Individual variations of total and percent free serum prostatic specific antigen: Could they change the indication of prostatic biopsy?

The aim of this study was to analyse the individual variations of total and percent free serum prostatic specific antigen (PSA) and to evaluate whethe r they could change the indication for prostatic biopsy. Prostatic needle b iopsy was indicated in 63 patients with serum PSA between 4.0 and 10 ng/ml. A new determination of total and free PSA was done before the biopsy proce dure. The time between the determinations ranged from 29 to 59 days. The to tal and free serum PSA determinations were performed by a double monoclonal antibody radioimmunoassay Tandem and Tandem free PSA. The median coefficie nt of variation for serum PSA was 12.9 in cancer free patients and 18.8 whe n cancer was detected, it was 32.6 and 42.2 respectively for percent free s erum PSA. A 22.8% rate of discrepancy between the determinations was found when prostatic biopsy was indicated only by percent free PSA lower than 25. Sensitivity ranged from 93.3% to 100, and reduction of unnecessary biopsie s between 15.2 and 21.8%. We conclude that individual variations in total a nd percent free serum PSA could have clinical implications because of the p ossibility that it changes the indication for a prostatic biopsy.