20-25% lower concentrations of total and free prostate-specific antigen (PSA) after calibration of PSA assays to the WHO reference materials – analysis of 1098 patients in four centers

Abstract

To examine the potential clinical implications of the recalibration of total prostate-specific antigen (PSA) and free PSA (fPSA) assays to the World Health Organization (WHO) standard materials. Data from 1098 patients with or without clinically detected prostate cancer (PCa) from four independent cohort studies were compared using commercial assays calibrated to the traditional Hybritech PSA (PSA-Hyb) and fPSA (fPSA-Hyb) standards and to the WHO 96/670 (PSA-WHO) and 96/668 (fPSA-WHO) standards. The Access Immunoassay System (Beckman Coulter, Inc.) was used in all studies. All studies showed 20% to 25% lower PSA and fPSA test results with the WHO-standardized assays. No significant change in %fPSA (fPSA/PSA x 100) was observed. Continuing to use the traditional clinical PSA cutoffs obtained with the Hybritech standard after changing to the PSA-WHO standard could result in up to one-third of prostate cancer cases being missed. Manufacturers should fully inform laboratories about a calibration change and its clinical impact. Laboratory reports for PSA measurements should indicate the assay's manufacturer and which calibration standard was used to avoid misleading information concerning PCa risk.