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

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. According to EP17-A, serum pools of anonymous routine patient samples residuals were analyzed on a UniCelDxI800 with the chemiluminescent Access®Hybritech®TotalPSA assay. We obtained the following results: LoB: 0.0046 μg/L Hybritech, 0.005 μg/L WHO calibration; LoD: 0.014 μg/L Hybritech, 0.015 μg/L WHO; LoQ at 20% coefficient of variation (CV%) 0.0414 μg/L Hybritech, 0.034 μg/L WHO. Regression Hybritech y=0.2398×+4.2017 (R2=0.9515); WHO y=0.2248×+3.4335 (R2=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). 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.