Comparison of cardiac TnI outliers using a contemporary and a high-sensitivity assay on the Abbott Architect platform

Abstract

Background: Assays for cardiac troponin (cTn) have undergone improvements in sensitivity and precision in recent years. Increased rates of outliers, however, have been reported on various cTn platforms, typically giving irreproducible, falsely higher results. We aimed to evaluate the outlier rate occurring in patients with elevated cTnI using a contemporary and high-sensitivity assay. Methods: All patients with elevated cTnI (up to 300 ng/L) performed over a 21-month period were assayed in duplicate. A contemporary assay (Abbott STAT Troponin-I) was used for the first part of the study and subsequently a highsensitivity assay (Abbott STAT High-Sensitive Troponin-I) was used. Outliers exceeded a calculated critical difference (CD) (CD ¼ z ¡2  SD Analytical ) where z ¼ 3.5 (for probability of 0.0005) and critical outliers also were on a different side of the decision level. Results: The respective outlier and critical outlier rates were 0.22% and 0.10% for the contemporary assay (n ¼ 4009) and 0.18% and 0.13% for the high-sensitivity assay (n ¼ 3878). There was no significant reduction in outlier rate between the two assays ( 2 ¼ 0.034, P ¼ 0.854). Fifty-six percent of outliers occurred in samples where cTn was an 'add-on' test (and was stored and refrigerated prior to assay). Conclusion: Despite recent improvements in cTn methods, outliers (including critical outliers) still occur at a low rate in both a contemporary and high-sensitivity cTnI assay. Laboratory and clinical staff should be aware of this potential analytical error, particularly in samples with suboptimal sample handling such as add-on tests.

Discordance with 3 Cardiac Troponin I and T Assays: Implications for the 99th Percentile Cutoff

“…The possibility of outliers owing to a random analytical failure or to sample-specific interference by heterophile or other antibody interference has been raised as a possible cause of falsely increased cardiac troponin (2 ). Our duplicate testing protocol with the Beckman Coulter assay eliminated the possibility of random outliers with this assay and the reported rates of these with the Roche cTnT (0.02%) and Abbott cTnI (0.18%) were too low to explain the discordance found (7,15 ). Although we did not systematically test all samples for heterophile antibody interference, we did exclude 1 sample that interfered with the Beckman Coulter assay.…”

High incidence of macrotroponin I with a high-sensitivity troponin I assay

“…In these cases the presence of macrotroponin was proven by a panel of investigations. False-positive cTnI immunoassay results may be caused by factors other than macrotroponin, including interfering antibodies, fibrin microclots, carryover, random error and haemolysis [29][30][31][32].…”

Analytical robustness of nine common assays: frequency of outliers and extreme differences identified by a large number of duplicate measurements

“…Outliers are differently defined in the literature and their frequencies are reported by various approaches ( 1 , 2 , 4 , 5 , 16 - 19 , 23 - 26 ). Additionally, what is perceived as an outlier may vary depending on the analyte or diagnosis ( 2 , 4 , 16 - 19 , 24 , 27 ).…”