Comparison of two investigative assays for the complexed prostate-specific antigen in total prostate-specific antigen between 4.1 and 10.0 ng/mL

Abstract

Objectives. To determine the ability of complexed prostate-specific antigen (cPSA) levels to diagnose prostate cancer. Methods. Between September 1998 and March 1999, cPSA levels in 182 consecutive patients with an abnormal digital rectal examination (DRE) or a total PSA (tPSA; Tandem-R assay) level greater than 4.1 ng/mL were examined. Levels of cPSA were measured by the Markit-M PSA-ACT (alpha 1-antichymotrypsin) assay (cPSA-MM) and Bayer Immuno 1 complexed PSA assay (cPSA-BI). Free PSA (fPSA) was measured by the Tandem-R free PSA assay. Results. Of the 140 patients with tPSA between 4.1 and 10.0 ng/mL, 116 were histologically confirmed as having benign tissue; the remaining 24 were diagnosed with prostate cancer. To ensure a 92% sensitivity of cancer detection, a cutoff value for the tPSA, cPSA-MM, and cPSA-BI assays of 4.8 ng/mL, 2.7 ng/mL, and 4.6 ng/mL, respectively, was determined. The percentage of negative biopsies prevented at these cutoff (ie, specificity) values was 14%, 23%, and 24%. No significant differences among these three assays were found. At 92% sensitivity, the cutoff value for the fPSA/tPSA, fPSA/cPSA-MM, and fPSA/cPSA-BI ratios was 18%, 27%, and 18%, respectively. The specificity was 35%, 49%, and 51%. No significant differences were found among these three fPSA ratios. Significant differences were noted between tPSA and the fPSA/cPSA-MM ratio and between tPSA and the fPSA/cPSA-BI ratio. No differences were seen among the other PSA parameters. Conclusions. No difference in the ability of cPSA levels to distinguish prostate cancer and noncancer was observed between cPSA-MM and cPSA-BI or between their fPSA ratios. Only the fPSA/cPSA-MM and fPSA/cPSA-BI ratios provided significantly enhanced diagnostic performance compared with tPSA.