title: Value of cardiac troponin I cutoff concentrations below the 99th percentile for clinical decision-making.
abstract: 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 microg/L to 0.028 microg/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.
authors.affiliation: Department of Medical Sciences, Uppsala University Hospital, Sweden. kai.eggers@ucr.uu.se
authors.forename: Kai M
authors.initials: KM
authors.lastname: Eggers
authors.forename: Allan S
authors.initials: AS
authors.lastname: Jaffe
authors.forename: Lars
authors.initials: L
authors.lastname: Lind
authors.forename: Per
authors.initials: P
authors.lastname: Venge
authors.forename: Bertil
authors.initials: B
authors.lastname: Lindahl
mesh_terms: D000368:Aged; D002318:Cardiovascular Diseases / Q000097:blood* / Q000175:diagnosis* / Q000401:mortality; D015510:Clinical Medicine; D015331:Cohort Studies; D003657:Decision Making; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011379:Prognosis; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012727:Sex Characteristics; D016019:Survival Analysis; D019210:Troponin I / Q000097:blood*
chemical_list: D019210:Troponin I