Objectives: To evaluate the ability of free/total prostate-specific antigen (PSA) ratio to improve specificity of prostate cancer detection, compare Diagnostic Products Corporation (DPC) Immulite and Ciba Corning ACS 180 total (t)PSA assay, and define an assay-specific cutoff point and reflex range for DPC PSA ratio (PSAR).
Methods: In a prospective study, 206 men were enrolled with measurement of both assays. Group 1 consisted of 173 men with a suspicion of prostate cancer (PCA). Thirteen men with known PCA (group 2) and 20 men younger than 32 years (group 3) were used as control groups.
Results: Our results in group 1 (115 with benign prostatic hyperplasia [BPH], 58 with PCA) revealed a sensitivity of 82.7%, a specificity of 45.2%, and an accuracy of 57.8% for the DPC tPSA assay (cutoff point more than 4.0 ng/mL) within the entire PSA range. tPSA values of the ACS 180 assay were 1.97-fold higher. Within the tPSA gray zone of 2.5 to 10 ng/mL (66 BPH, 23 PCA), specificity and accuracy of DPC tPSA can be improved by using the DPC PSAR (cutoff point less than 19%) from 33.3% to 71.2% and 42.7% to 70.8%, respectively, maintaining the same sensitivity level of 69.6%.
Conclusions: By combining tPSA testing with PSAR within the gray zone, 39.7% (25 of 63) of unnecessary biopsies can be saved, without missing any additional cancers compared with tPSA testing alone. The optimal reflex range for DPC PSAR is 2.5 to 10 ng/mL and the best PSAR cutoff point for biopsy criterion is less than 19% in our high-risk population, with a cancer yield of 34%. Because we still do not have an international PSA standard, it is important to use assay-specific "normal values" and PSAR cutoff points.