Background: Traditional methods of using creatinine kinase (CK)-MB to diagnose acute myocardial necrosis rely on the total CK-MB exceeding a threshold of normalcy before being considered diagnostic. Because the CK-MB rapid immunoassay is both sensitive and precise, a small difference between two serial samples over an appropriate time interval may result in an increased sensitivity for acute myocardial infarction (AMI) compared with traditional methods if an appropriate cutoff value is chosen.
Methods and results: Baseline and 2-hour CK-MB immunoassay measurements were performed in 710 patients with chest pain whose baseline CK-MB was less than two times upper limits of normal (<12 ng/ml) to determine whether a rise in CK-MB > or =+1.6 ng/ml is more sensitive and specific than an abnormal 2-hour CK-MB in the detection of patients with AMI during the initial emergency department evaluation of chest pain. The baseline (MBO) or 2-hour (MB2) CK-MB was considered positive if the CK-MB level was > or =6 ng/ml. MBdelta was defined as the difference of MB2 and MBO and was considered positive if the value was > or =+1.6 ng/ml. A positive MB2 was more sensitive for the detection of AMI (75.2% vs 17.7%; p < 0.0001) than a positive MBO. A positive MBdelta was more sensitive for the detection of AMI (93.8% vs 75.2%; p < 0.0001 ) than a positive MB2. There were no statistically significant differences in specificities for AMI for any test modality.
Conclusions: A rise in CK-MB of > or =+ 1.6 ng/ml in 2 hours is a useful marker of AMI during the initial emergency department evaluation of patients with chest pain.