EVALUATION OF A NEW RAPID QUANTITATIVE IMMUNOASSAY FOR SERUM MYOGLOBIN VERSUS CK-MB FOR RULING OUT ACUTE MYOCARDIAL-INFARCTION IN THE EMERGENCY DEPARTMENT

Study objective: To compare the predictive values of serum myoglobin a nd creatine kinase (CK)-MB for ruling out acute myocardial infarction in the emergency department. Design: Prospective, observational study. Setting: University teaching hospital. Participants: One hundred eigh ty nine consecutive patients aged 30 years and older who presented wit hin 12 hours from onset of chest discomfort, dyspnea, syncope, congest ive heart failure, symptomatic dysrhythmia, pulmonary edema, or epigas tric pain were entered into the study. Patients with trauma or renal f ailure were excluded. Interventions: Standardized history and physical examination and blood sampling for serum myoglobin (S-Mgb) and CK-MB were done at the time of presentation (T0) and 1 hour later (T1). Resu lts: Using World Health Organization criteria, 22 acute myocardial inf arction patients were identified. Mean time from symptom onset to pres entation was 3.2 hours. S-Mgb was more sensitive than CK-MB at T0 and T1, 55% versus 23% (P<.05) and 73% versus 41% (P<.05), respectively. R espective specificities of S-Mgb versus CK-MB were 98% versus 99% (P=N S) at T0 and 97% versus 99% (P=NS) at T1. Negative predictive values o f S-Mgb versus CK-MB were 94% versus 91% (P=NS) at T0 and 96% versus 9 3% (P=NS) at T1. The S-Mgb assay yielded quantitative results allowing the difference between the T0 and T1 values to be analyzed. A differe nce of 40 or more ng/mL between T0 and T1 was considered positive. Whe n using a positive result in either the T0 or T1 value or a difference between the two values of 40 or more ng/mL, the sensitivity of S-Mgb was 91% (P<.05 versus CK-MB), the specificity was 96% (P=NS versus CK- MB), and the negative predictive value was 99% (95% confidence interva l for S-Mgb, 97.0 to 100 versus CK-MB, 95% confidence interval, 88.9 t o 96.6). Conclusion: In the first hour of presentation to the ED, the rapid quantitative assay for S-Mgb was statistically more sensitive th an CK-MB and had an excellent negative predictive value for ruling out acute myocardial infarction in patients with typical or atypical symp toms. Due to the relatively small sample size, we could not exlude the possibility that differences in specificity might become statisticall y significant (beta error) with a larger sample size of acute myocardi al infarction patients.