Creatine kinase-MB does not add additional benefit to a negative troponin in the evaluation of chest pain

Objective

The aim of this study was to determine whether current troponin assay alone can be used for initial screening for acute myocardial infarction (AMI) and whether creatine kinase-MB (CK-MB) can safely be eliminated from this evaluation in the emergency department (ED).

Methods

A retrospective cohort study of patients who had cardiac troponin T (Roche, Basel, Switzerland) and CK-MB ordered at an urban academic level 1 trauma center with more than 55,000 annual visits. Patients with troponin testing in the ED were identified over a period of 12 months, and corresponding CK-MB indexes were examined identifying patients with negative troponins (<0.01) and positive CK-MB indexes (>6.0). In these patients, further cardiac markers, hospital course, and 30-day mortality were then evaluated. A 99% confidence interval around point estimate was used in data analysis.

Results

During the study period, there were 11,092 separate ED patient encounters where a patient had at least one troponin resulted. Most (97.9%) of the samples had an associated CK-MB ordered. There were 7545 initial negative troponins representing 68% of all initial samples. Seven of these had an associated positive MB index. When subsequent troponins were evaluated, an additional 4910 negative troponins were identified, with 4 patients having a positive MB. None of these 11 patients were judged to have ruled in for AMI by the treating physicians. The rate of true-positive CK-MB index with negative troponin was 0% (99% confidence interval, 0-0.04%).

Conclusion

Our results suggest that CK-MB is not necessary in the initial screening for AMI and may safely be omitted in patients with negative troponins.