Background: The European Society of Cardiology/ American College of Cardiology (ESC/ACC) consensus document for definition of myocardial infarction (MI)is predicated on increased cardiac troponin or creatine kinase (CK) MB mass above the 99th percentile reference limit. The purpose of this study was to determine the plasma (heparin) 99th percentile reference limits for the leading in vitro diagnostic cardiac troponin and CKMB mass assays. Methods: Blood (heparin plasma) was obtained from healthy adults (n ؍ 696; age range, 18 -84 years) stratified by gender and ethnicity. Cardiac troponin I (cTnI) and T (cTnT) and CKMB mass concentrations were measured by eight assays. Reference limits were determined by nonparametric statistical analysis. Results: Two cTnI assays demonstrated at least a 1.2-to 2.5-fold higher 99th percentile for males vs females, with the mean concentrations significantly higher for males (P <0.05). Two cTnI assays also demonstrated a 1.1-to 2.8-fold higher 99th percentile for blacks vs Caucasians, with the mean concentrations significantly higher for blacks (P ؍ 0.05). There was a 13-fold variance between the lowest measured 99th percentile (0.06 g/L) and the highest (0.8 g/L). All CKMB assays demonstrated a 1.2-to 2.6-fold higher 99th percentile for males vs females, with mean concentrations signifi-
Cardiac troponin (cTn) assays were compared in 490 unselected patients with symptoms suggestive of acute coronary syndrome with varying renal functions for risk stratification. cTnI (Dade, Newark, NJ; Beckman, Chaska, MN; and Tosoh, South San Francisco, CA) and cTnT (Roche, Indianapolis, IN) measurements and estimated glomerular filtration rates (eGFRs) were obtained and classified along sex-derived cutoffs. The cTn levels were increased in 14% to 25% of patients. In 68%, the eGFR was 60 mL/min/1.73 m2 or more; in 17%, it was between 41 and 59; and in 15%, it was 40 or less. There were 36 deaths and 9 cardiac events. Risk stratification was significant at 30 days and 6 months (P < or = .05). Relative risks ranged from 3.1 to 3.7, and cumulative event rates ranged from 22.4% to 24.2% for an increased troponin level compared with 6.7% to 8.9% for a normal level. The 6-month event rate with an eGFR less than 60 mL/min/1.73 m2 and an increased troponin level ranged from 29.9% to 50.8% compared with 4.9% to 6.6% for a normal troponin level and an eGFR greater than 60 mL/min/1.73 m2 (P < .05). The eGFR in combination with an increased cTn level demonstrated the most powerful stratification.
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