FREE AND COMPLEXED PROSTATE-SPECIFIC ANTIGEN IN THE DIFFERENTIATION OF BENIGN PROSTATIC HYPERPLASIA AND PROSTATE-CANCER - STUDIES IN SERUM AND PLASMA SAMPLES

Purpose: We prospectively evaluated serum and plasma concentrations of total and free prostate specific antigen (PSA), and PSA complexed to al-antichymotrypsin in 170 patients who underwent biopsy, including 59 with prostate cancer and 111 with benign prostatic hyperplasia. We co mpared the usefulness of the ratios of free-to-total and complexed-to- total PSA for distinguishing between prostate cancer and benign prosta tic hyperplasia, and studied the influence of blood clotting on the ra tios. Materials and Methods: Blood samples were processed to generate serum and citrated plasma. To calculate complexed-to-total and free-to -total PSA we assayed plasma and serum samples for total and complexed PSA using homemade immunoassays, and total and free PSA using the Imm ulite assay. The 2 total PSA assays were compared using the Tandem-E dagger PSA assay. Receiver operating characteristics curves were const ructed for the total population, and for 2 to 20, 4 to 20, 2 to 10 and 4 to 10 ng./ml. total PSA. Results: In all groups complexed-to-total PSA had higher specificity than free-to-total and total PSA, especiall y at 90 to 100% sensitivity. Generally citrated plasma samples provide d higher specificity than serum samples for all sensitivity values. Th e best performance for complexed-to-total and free-to-total PSA was ob tained in the subset of patients in whom total PSA was 2 to 10 ng./ml. Conclusions: Our results indicate that the complexed-to-total PSA rat io performed better for classifying disease status than the free-to-to tal PSA ratio in the whole patient population and in the diagnostic gr ay zone of 2 to 10 ng./ml. In addition, plasma samples should be used to calculate the complexed-to-total and free-to-total PSA ratio.