A training program was scheduled before the beginning of the experiment to ensure that the operators would understand all procedures and could execute them properly . High sensitive troponin I assays (hsTnI) (Access hsTnI, Beckman Coulter, Brea, CA, USA) were performed on sera from anonymized pre-existingheparin-plasma samples with a TnI (AccessAccuTnI+3, Beckman Coulter, Brea, CA, USA) result. Tests were processed sequentially on the two DxI800 (Beckman Coulter), DxI-1 and DxI2, found in the stat laboratory, and on the other, DxXI-3, found in the central routine laboratory.

We used the hsTnI (Access hsTnI, Beckman Coulter, Brea, CA, USA) assay, which is characterized by a 2.3 ng/L LoD, 11.6 ng/L 99th percentile for women (CV%: 4.2), 19.8 ng/L 99th percentile for men (CV%: 3.6), 17.5 ng/L 99th percentile for overall (CV%: 3.7) and the 10%CV at 5.6 ng/L. Evaluation of total imprecision.

Total imprecision within the laboratory, expressed by the coefficient of variation (CV%), were calculated on all instruments. This was done by running five replicates of a plasma pool (P) (concentration of approximately 21 ng/L) and three internal quality controls (IQC) (Biorad Liquichek Cardiac Markers plus Control LT, Level 1C (CQ-LC) at approximately 17 ng/L, Biorad Level 1 (CQ1), at approximately 42 ng/L and Biorad Level 2 (CQ2), at approximately 780 ng/L) for five times [14]. These analyses were performed over a period of three weeks. Grubbs’ test was used to evaluate the presence of outliers [14]. In addition, daily IQC were evaluated before starting all analytical sessions (IQC-LC, IQC1, IQC2). Same lot of reagents were used over the experimental period (of about two months) and were calibrated using two different calibrator lots.

the measurements, and Bland-Altman technique to estimate the consistency of the methods[13,15,16]. The results given by the three instruments were analyzed as followed: DxI1 vs. DxI2, DxI1 vs. DxI3, DxI2 vs. DxI3. The statistical analysis was inclusive of all the results, but this study focuses on the subgroup characterized by values below 50 ng/L. The acceptance of inter-identical-instrument bias calculated with the Bland-Altman test (bias ± 95%CI limits of agreement) was based on the reference change values (RCV= 2.77 (CVa2 + CVi2 ) 1/2 where CVi=intra individual variation, taken as 10% and CVa=total imprecision). Finally, method comparisonwas evaluated by means of the weighted Cohen’s Kappa statistic

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Denise Williams
Managing Editor
Biomarkers Journal