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

Proteomics and Protein Markers

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

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 Troponin I 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.

Kai M. Eggers1,a, Allan S. Jaffe4, Lars Lind2, Per Venge3 and Bertil Lindahl1

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

An evaluation of the association between C-reactive protein, the change in C-reactive protein over one year

Objectives. To evaluate the association between systemic inflammation, as measured by C-reactive protein , and all-cause mortality. To also evaluate the association between change in CRP status (sub-acute, 10 mg/l and acute >10 mg/l) and all-cause mortality.

Methods. A cohort of patients was selected from The Health Improvement Network (THIN) data set of anonymized patient-level data from UK general practice. Patients were selected if they had a diagnosis of RA, psoriasis, AS or PsA. Survival was evaluated using Cox proportional hazards regression models (CPHMs).

Results. A total of 11 362 cases had at least one CRP measurement. Analysis grouped by each additional unit increase in log-CRP (range 1–6) across the observed range was associated with a 21% increase in the hazard ratio (HR) of death, after controlling for cardiovascular risk factors (P < 0.001). This observation was consistent in separate analysis of cases with either RA or psoriasis. Repeated CRP observations around 1 yr apart were recorded in 2802 subjects. After controlling for confounding factors, in cases whose CRP changed from sub-acute (10 mg/l) to acute (>10 mg/l), the HR for death increased 2-fold (P < 0.001) relative to cases whose CRP remained sub-acute. In comparison, among those subjects whose CRP was reduced from acute to sub-acute, the HR was virtually identical to those who stayed sub-acute (P = 0.571).

Conclusions. CRP level predicted all-cause mortality after standardization for traditional risk factors, as did change in CRP status from sub-acute to acute observed over 1 yr.