Comparing analytical outliers and the percent of emergency department patients with results above the 99th percentile upper reference limit for 2 conventional and one high sensitivity troponin assay

Objectives: We compared rates of analytical outliers, and percent of emergency department (ED) patients with cardiac troponin (cTn) values above the 99th percentile upper reference limit (URL), for two conventional and one high sensitivity cTn assay. Methods: We measured 3008 samples from 1931 ED patients by Roche e411 4th generation Troponin T (cTnT); and Abbott STAT Troponin I (cTnI) and high sensitivity troponin I (hscTnI) on an Architect i2000. Within 24 h of initial measurement, samples were aliquoted, re-centrifuged, and repeated in duplicate by all methods. Outliers were defined as one or both replicates exceeding initial value by a critical difference (CD): where CD=z×2×SDanalytical (z = 3.29 at a probability of 0.0005), and at least one replicate on a different side of 99th percentile URL compared to initial value. We also assessed percent of ED patients with values > 99th percentile by all methods (excluding outliers), using both sex-neutral and sex-specific hscTnI URL. Results: The outlier rate for cTnI (3.66%) was significantly higher than the outlier rate for either cTnT (0.33%) or hscTnI (0.47%) (p < 0.0001). More ED patients (33%) had elevated cTnT values compared to either cTnI (25%) or hscTnI (29%). Application of sex-specific URL did not change the percent of ED patients with > 99th percentile hscTnI values. Conclusion: Abbott STAT cTnI had more analytic outliers than Roche cTnT or Abbott hscTnI. Compared to cTnT, use of hscTnI will significantly decrease the percent of ED patients with elevated cTn values without increasing analytical outliers.