Analytical performance and clinical validity of two free prostate- specific antigen assays compared

Abstract

We compared two recently introduced commercial assays (CanAg and Immulite) for measuring free prostate-specific antigen (f-PSA), total PSA (t- PSA), and the ratio of t-PSA/f-PSA (f-PSA%) in control materials and sera of 54 healthy men, 50 patients with benign prostatic hyperplasia (BPH), and 45 patients with prostate cancer (PCa). The lower detection limits for f-PSA were 0.038 μg/L and 0.004 μg/L for the CanAg and Immulite assays, respectively. The within-run and between-day precisions of the Immulite assay were <5%; the CanAg assay showed a poorer precision. Whereas f-PSA values differed between controls and patients but not between BPH and PCa patients, the f-PSA% values were lower in PCa patients than in BPH patients and controls. The receiver-operating characteristic (ROC) curve showed an improved diagnostic power of f-PSA% compared with t-PSA to discriminate between BPH and PCa. Discrimination limits of 16% (CanAg assay) and 15% (Immulite assay) are recommended for f-PSA%.