Study objective: We evaluated the diagnostic accuracy of myoglobin determination for the early diagnosis of acute myocardial infarction (AMI).
Methods: Consecutive patients with chest pain were included in the study. Receiver operating characteristic (ROC) analysis was used to assess optimal timing of blood sampling and cutoff values.
Results: A total of 309 patients were included, of whom 162 patients had a diagnosis of AMI. ROC analysis revealed that the diagnostic accuracy of myoglobin concentration as indicated by the area under the ROC curve (AUC) increased significantly from 3 (0.89+/-0.026) and 4 hours (0.93+/-0.019) to 5 hours after onset of symptoms (0. 96+/-0.014; P=.0040 and.035, respectively). At 5 hours (the earliest time point with maximal AUC), sensitivity was 87% and specificity was 97% using a myoglobin cutoff value of 90 microg/L. With a myoglobin cutoff value of 50 microg/L, sensitivity was 95% (95% confidence interval 90% to 98%), but specificity was 86% (95% confidence interval 80% to 93%).
Conclusion: Myoglobin has maximal diagnostic accuracy for the diagnosis of AMI at 5 hours after the onset of symptoms, using a cutoff value of 50 microg/L. In combination with the measurement of other biochemical markers, myoglobin determination could be particularly useful for triage of patients with AMI at an early stage.