CLSI EP17-A protocol: A useful tool for better understanding the low end performance of total prostate-specific antigen assays

Abstract

Background: Clinical Laboratory and Standards Institute (CLSI) published EP17-A guideline, recommending new definitions for low end performances: Limit of Blank (LoB), Limit of Detection (LoD) and Limit of Quantitation (LoQ). The aim of this study was to determine LoB, LoD and LoQ by applying EP17-A to Hybritech and World Health Organization (WHO) calibrated Access Total PSA assays, and verify the correlation between results generated by the same reagent with both calibrations, particularly at low end concentrations. Methods: According to EP17-A, serum pools of anonymous routine patient samples residuals were analyzed on a UniCelDxI800 with the chemiluminescent Access®Hybritech®TotalPSA assay. Results: LoB: 0.0046μg/L Hybritech, 0.005μg/L WHO calibration; LoD: 0.014μg/L Hybritech, 0.015μg/L WHO; LoQ at 20% coefficient of variation (CV%) 0.0414μg/L Hybritech, 0.034μg/L WHO. Regression Hybritech y=0.2398×+4.2017 (R 2=0.9515); WHO y=0.2248×+3.4335 (R 2=0.9596) with no statistical difference. Comparison between Hybritech and WHO at low PSA levels indicated an excellent Pearson's and intraclass correlation (r=0.999, p<0.001; ICC=0.974, p<0.001). Conclusions: Our results show that the Access Total PSA assay is suitable for prostate cancer recurrence and PSA velocity evaluation; Hybritech and WHO calibrated values can both be used for clinical purposes even at low levels. © 2011 Elsevier B.V.