Could the Intra-Laboratory Inter-Identical-Instrument Bias Compromise the Interpretation of the Absolute High-Sensitive Troponin Delta Around the 99th Percentile Upper Reference Limit?

Aim of the study: To measure high-sensitive troponin (Access hsTnI) interidentical- instrument bias (DxI800 Beckman Coulter) in order to understand if it can compromise the interpretation of absolute delta value for rapid algorithms 0/1-0/3 hours. Materials and methods: One hundred fifty-nine lithium/heparin plasma samples were processed sequentially on three DxI800 (DxI1, DxI2, DxI3). The results given by the three instruments were analyzed as followed: DxI1 vs. DxI2, DxI1 vs. DxI3, DxI2 vs. DxI3. Statistical analysis was done using the Passing-Bablok regression, Bland-Altman test, and Cohen’s Kappa statistic. Results: PB regression did not show any significant deviation from linearity and no proportional nor constant differences were observed among instruments. Moreover, the mean absolute bias, even though among the three instruments the lowest 95%CI lower limit was -3.75 and the highest 95%CI upper limit was 3.92 ng/L, was within the acceptance limits (all results<reference change value). The concordance between each couple of instruments was mostly strong. Conclusion: Our data suggest that inter-identical-instrument bias needs to be considered before evaluating the clinical diagnostic accuracy of one absolute delta with respect to another, in order to define the minimum absolute delta that the laboratory can guarantee to the clinicians.