Early 'rule-in' diagnosis of acute myocardial infarction 4 h post admission for rapid risk stratification by creatine kinase increment (creatine kinase change).

The use of creatine kinase (CK) measurement on admission, CK at 4 h, percentage CK change and electrocardiography (ECG) were compared for early risk stratification in the diagnosis of acute myocardial infarction (AMI). A total of 248 patients (median age 62 years, range 26-84) were studied (187 men, 61 women) of whom 118 had a final diagnosis of AMI. Median time to presentation was 3.92 h (range 0-11.17 h). Overall, the admission ECG had a sensitivity of 72.6% [95% confidence interval (CI) 64.6-80.7] with specificity of 88.9% (CI 83.4-94.4); 4 h CK change had a sensitivity of 100% (CI 96.1-100) with a specificity of 90.4% (CI 83.5-95.1). After excluding those with contraindication to anti-thrombotic therapy there were 109 patients with an uncertain initial diagnosis. In this group, admission CK had a sensitivity of 37.5% (CI 18.8-59.4) with a specificity of 94% (CI 86.8-98.1); 4 h ECG had a sensitivity of 43.8% (CI 19.8-70.1) with specificity of 97.4% (CI 86.5-99.9%); 4 h CK had a sensitivity of 79.2% (CI 57.8-92.9) with a specificity of 96.5% (CI 90-99.3); 4 h CK increment had a sensitivity of 100% (CI 85.8-100) with a specificity of 94% (CI 86.8-98.1). The admission ECG remains the investigation of choice for early 'rule-in' diagnosis of AMI for thrombolysis. Admission measurement of CK offers a small advantage in the patient with an uncertain diagnosis but the overall benefit is low. A strategy of admission ECG plus serial testing allows diagnosis to be complete by 4 h for accurate risk stratification. Whether this can be used for selection for therapeutic options (thrombolytic, anti-coagulation, anti-platelet or anti-anginal agents) requires further clinical trials.