Macrocomplex Detection Differs Between High-Sensitivity Cardiac Troponin I Assays

The standard test for detecting myocardial injury, assessment of high-sensitivity cardiac troponin I (hsTnI), has been shown to give discordant results between test suppliers. The implications of this fact were discussed in a Letter to the Editor published in the Canadian Journal of Cardiology.

Excess paired lithium heparin and EDTA plasma samples (N=209) were retested by Ortho Clinical Diagnostics and Abbott Diagnostics hsTnI assays. The median percent difference of concentrations between tests was calculated for all results that had a concentration of more than10 ng/L for at least one of the tests or fold differences between the Ortho and Abbott results either less than 0.33 or more than 2.0.

The Ortho hsTnI assay consistently reported concentrations 30% to 50% below the Abbott hsTnI assay for both the lithium heparin samples (median percent difference, -38%; 95% CI, -44% to -33%) and the EDTA samples (median percent differences, -49%; 95% CI, -53% to -43%).

A total of 12 patients had concordant results; 11 samples had an Ortho-to-Abbott ratio of less than 0.33 and 4 had a ratio greater than 2.0. Among the 12 patients with concordant results, 9 had detectable macrocomplexes from at least one of the tests and the other 3 patients did not.

There was a disagreement between lithium heparin and EDTA test results among 11 patients. These patients had stroke or subarachnoid hemorrhage (n=4), syncope (n=3), discordant results following noncardiac surgery (n=3), atrial fibrillation (n=1), and patent dyspnea (n=1).

It has been established that macrocomplexes of immunoglobulin-bound cardiac troponin may yield high hsTnI concentrations among some patients and that the Ortho Clinical Diagnostics hsTnI assay was more likely to have low recovery and the Abbott Diagnostics hsTnI assay was more likely to have higher recovery of these macrocomplexes.

The observed analytical discordances presented here, however, cannot fully be explained by the variation between manufacturer detection of macrocomplexes. The letter authors concluded that problematic samples, which have contradictory results from the lithium heparin and EDTA tests, may need to be tested by other hsTnI assays.

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.

Reference

Kavsak PA, Ainsworth C, Worster A. An approach to investigate discordant high-sensitivity cardiac troponin I results. Can J Cardiol. 2020;S0828-282X(20)31106-5. doi:10.1016/j.cjca.2020.11.005