Abstract
Objectives: We investigated absolute and relative cardiac troponin I (TnI) delta changes, optimal sampling protocols, and decision thresholds for early diagnosis of myocardial infarction (MI). Serial cardiac biomarker values demonstrating a rise and/or fall define MI diagnosis; however the magnitude of change, timing, and diagnostic accuracy of absolute versus relative (percentage) deltas remains unsettled. Methods: We prospectively measured TnI (AccuTnI. +. 3™, Beckman Coulter) at serial time intervals in 1929 subjects with chest pain or equivalent symptoms of acute coronary syndrome at 14 medical centers. Diagnosis was adjudicated by an independent central committee. Results: Elevated TnI above a threshold of 0.03. ng/mL demonstrated significant diagnostic efficacy (AUC 0.96). For patients with TnI. <. 0.03. ng/mL and symptom onset. ≥. 8. h, 99.1% (NPV) were diagnosed with conditions other than MI. Absolute delta performed significantly better than relative delta at 1-3. h (AUC 0.84 vs 0.69), 3-6. h (0.85 vs 0.73), and 6-9. h (0.91 vs 0.79). Current recommendations propose ≥. 20% delta within 3-6. h; however, results were optimized using an absolute delta of 0.01 or 0.02. ng/mL. Sensitivity results for absolute delta at 1-3. h and 3-6. h (75.8%, 78.3%) were superior to relative delta (48.0%, 61.3%). NPV (rule out) was 99.6% when baseline TnI. <. 0.03. ng/mL and absolute delta TnI. <. 0.01. ng/mL. Conclusions: Absolute delta performed significantly better than relative delta at all time intervals. Baseline TnI and absolute delta may be used in conjunction to estimate probability of MI. Consensus recommendations are supported for sampling on admission and 3. h later, repeated at 6. h in patients when clinical suspicion remains high. © 2014 The Canadian Society of Clinical Chemists.