Myoglobin in the Early Evaluation of Acute Chest Pain

Two thirds of patients hospitalized to rule out acute myocardial infarction (AMI) are eventually found to have a non-AMI diagnosis, whereas 2% to 8% of patients with AMI are inappropriately discharged from the emergency department. Myoglobin has been shown to increase within 2 to 3 hours of myocardial injury. This study evaluates the usefulness of myoglobin in acute chest pain. Serial blood samples were obtained from 89 suspected AMI patients evaluated in the emergency department. Testing included creatine kinase (CK), a creatine kinase isoenzyme (CK-MB), and myoglobin. Twenty five of 89 patients (28%) had a diagnosis of AMI. The sensitivity of myoglobin for the detection of AMI was 56% at the time of admission and 100% 2 hours after admission. Thirteen of 25 AMI patients (52%) had a positive myoglobin before increases in CK or CK-MB, including one patient discharged from the emergency department. More importantly, the negative predictive value for myoglobin at the time of admission was 83% and was 100% two hours after admission. This potential for 100% predictability in excluding AMI by the use of serial myoglobin determinations will be very helpful in the correct triage of patients presenting with acute chest pain.