Abstract 12104: Absolute and Relative Changes (Delta) in Troponin I for Early Diagnosis of Myocardial Infarction: Results of a Prospective Multicenter Trial

Objectives: To investigate absolute and relative cardiac troponin I (TnI) delta changes, optimal sampling protocols, and decision thresholds for early diagnosis of myocardial infarction (MI). Background: 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 1,929 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 50% of the URL in the case of non-elevated baseline levels; however, results were optimized using an absolute delta of 0.01 or 0.02 ng/mL when baseline TnI is elevated, and an ROC-curve-derived absolute delta of 0.01 ng/mL in the case of non-elevated baseline levels. Sensitivity results for absolute delta at 1-3h and 3-6h (75.8%, 78.3%) were superior to relative delta (48.0%, 61.3%). NPV (rule out) was 99.6% (95% CI: 98.7-99.9) when baseline TnI Conclusions: Absolute delta TnI performed significantly better than relative delta TnI at all time intervals, in particular demonstrating higher sensitivity than relative delta at an earlier time interval. Baseline TnI and absolute delta may be used in conjunction to estimate probability of MI. Consensus recommendations are supported for sampling on admission and 3h later; repeat measurements should be considered 6h after admission in patients for whom the 3h values are unchanged but clinical suspicion of MI is high, or time of symptom onset unknown.