EVALUATION OF A NEW ASSAY FOR CARDIAC TROPONIN-I VS CREATINE KINASE-MB FOR THE DIAGNOSIS OF ACUTE MYOCARDIAL-INFARCTION

To compare a new assay for cardiac troponin I (cTn-I) with an assay fo r creatine kinase-MB (CK-MB) for the diagnosis of acute myocardial inf arction (AMI). Methods: A prospective cross-sectional study of patient s presenting with symptoms consistent with cardiac ischemia was perfor med at a university teaching hospital. Serum sampling for cTn-I and CK -MB was performed at 0, 1, 3, 8, and 16 hours after presentation. Norm al values were defined as CK-MB less than or equal to 7 ng/mL and a re lative index less than or equal to 2%. cTn-I less than or equal to 1.4 ng/mL. Final diagnosis was made using World Health Organization crite ria, including standard enzyme sampling. Consecutive patients with AMI were compared with a randomly selected subset of patients without AMI to determine the sensitivity and specificity of the cTn-I and CK-MB a ssays for AMI, stratified by time from symptom onset. The ability of t he biochemical cardiac markers obtained within 6 hours of symptom onse t to predict later complications or need for interventions was assesse d using adds ratios (ORs). Results: Thirty-five patients who had AMI w ere compared with 136 patients who did not have AMI. The sensitivities and specificities of the cTn-I and CK-MB assays, stratified by time f rom symptom onset, were: [GRAPHICS] Patients who had elevations in eit her CK-MB or cTn-I within 6 hours of symptom onset were at increased r isk for cardiovascular complications and/or interventions (CK-MB, OR 5 .8; cTn-I, OR 6.3). Conclusion: cTn-I was as sensitive and specific fo r AMI as was CK-MB in ED patients who presented within 24 hours of sym ptom onset. However, cTn-I was more sensitive in patients who presente d greater than or equal to 24 hours after symptom onset. Elevations of either marker within 6 hours of symptom onset predict an increased ri sk of complications and/or need for interventions.