Free/total prostate-specific antigen ratio can prevent unnecessary prostate biopsies.

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.