1261 Clinical evaluation of specific assays for free PSA and total PSA

It is now well known that PSA assays measure simultaneously free PSA (FPSA) and PSA bound to α-1 antichymotrypsin (PSA-ACT). Furthermore specific measurement of the free form gives additional information on PSA in the distinction between benign prostate hypertrophies (BPH) and prostate cancer. In order to evaluate the contribution of free PSA in addition to that of total PSA, we tested 105 patients’ serum with prostate pathology (prostate cancer or BPH). All patients had a digital rectal examination, a total PSA measurement (values between 2 and 30 ng/ml) and possibly a biopsy as well. Results obtained showed that with the total PSA (cut-off 4 ng/ml), the measurement does not allow a good discrimination between BPH and prostate cancer (specificity of 46%). For this population (105 patients) the positive predictive value (PPV) of total PSA was only 48%. The use of free PSA measurement and the ratio of free PSA to total PSA (F/T PSA) allowed the PPV to rise to 87%. These first results showed that for the patient population which had given low specificity for a simple total PSA measurement (4 to 14 ng/ml), the ratio F/T PSA allowed the detection of 60% prostate cancer with a specificity of 95%.