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Value of Cardiac Troponin I Cutoff Concentrations below the 99th Percentile for Clinical Decision-Making

Departments of¹ Medical Sciences, Cardiology,² Medicine, and ³ Clinical Chemistry, Uppsala University Hospital, Sweden, and⁴ Mayo Medical School, Rochester, MN.

^aAddress correspondence to this author at: Department of Medical Sciences, Cardiology, University Hospital Uppsala, S-751 85 Uppsala, Sweden. Fax +46-18-50 66 38; e-mail kai.eggers{at}ucr.uu.se.

Background: The aim of this study was to evaluate factors influencing the 99th percentile for cardiac troponin I (cTnI) when this cutoff value is established on a highly sensitive assay, and to compare the value of this cutoff to that of lower cutoffs in the prognostic assessment of patients with coronary artery disease.

Methods: We used the recently refined Access AccuTnI assay (Beckman-Coulter) to assess the distribution of cTnI results in a community population of elderly individuals [PIVUS (Prospective Study of the Vasculature in Uppsala Seniors) study; n = 1005]. The utility of predefined cTnI cutoffs for risk stratification was then evaluated in 952 patients from the FRISC II (FRagmin and Fast Revascularization during InStability in Coronary artery disease) study at 6 months after these patients had suffered acute coronary syndrome.

Results: Selection of assay results from a subcohort of PIVUS participants without cardiovascular disease resulted in a decrease of the 99th percentile from 0.044 µg/L to 0.028 µg/L. Men had higher rates of cTnI elevation with respect to the tested thresholds. Whereas the 99th percentile cutoff was not found to be a useful prognostic indicator for 5-year mortality, both the 90th percentile (hazard ratio 3.1; 95% CI 1.9–5.1) and the 75th percentile (hazard ratio 2.8; 95% CI 1.7–4.7) provided useful prognostic information. Sex-specific cutoffs did not improve risk prediction.

Conclusions: The 99th percentile of cTnI depends highly on the characteristics of the reference population from which it is determined. This dependence on the reference population may affect the appropriateness of clinical conclusions based on this threshold. However, cTnI cutoffs below the 99th percentile seem to provide better prognostic discrimination in stabilized acute coronary syndrome patients and therefore may be preferable for risk stratification.

The following articles in journals at HighWire Press have cited this article:

				P. O. Collinson, O. Clifford-Mobley, D. Gaze, F. Boa, and R. Senior Assay Imprecision and 99th-Percentile Reference Value of a High-Sensitivity Cardiac Troponin I Assay Clin. Chem., July 1, 2009; 55(7): 1433 - 1434. [Full Text] [PDF]

				F. S. Apple A New Season for Cardiac Troponin Assays: It's Time to Keep a Scorecard Clin. Chem., July 1, 2009; 55(7): 1303 - 1306. [Full Text] [PDF]