EARLY DIAGNOSTIC EFFICIENCY OF CARDIAC TROPONIN-I AND TROPONIN-T FOR ACUTE MYOCARDIAL-INFARCTION

Objective: To compare the early diagnostic efficiency of the cardiac t roponin I (cTn-I) level with that of the cardiac troponin T (cTn-T) le vel, as well as the creatine kinase (CK), CK-MB, and myoglobin levels, for acute myocardial infarction (AMI) in patients without an initiall y diagnostic ECG presenting to the ED within 24 hours of the onset of their symptoms. Methods: A prospective, observational, cohort study wa s performed involving chest pain patients admitted to a large urban co mmunity hospital. Participants were consecutive consenting ED chest pa in patients greater than or equal to 30 years of age. Exclusions inclu ded duration of symptoms >24 hours, inability to complete data collect ion, receipt of CPR, and ST-segment elevation on the initial ECG. Meas urements included levels of cTn-I, cTn-T, CK, CK-MB, and myoglobin at the time of presentation and 1, 2, 6, and 12-24 hours after presentati on as well as presenting ECG and clinical follow-up. Confirmation of t he diagnosis of AMT was based on World Health Organization criteria. R esults: Of the 177 patients included in the study, 27 (15%) were diagn osed as having AMIs. The sensitivities of all 5 biochemical markers fo r AMI were poor at the time of ED presentation (3.7-33.3%) but rose si gnificantly over the study period. The sensitivity of cTn-T was signif icantly better than that of cTn-I over the initial 2 hours, but both m arkers' sensitivities were low (<60%) during this time frame. The cTn- I was significantly more specific for AMI than was the cTn-T, but not significantly better than CK-MB or myoglobin. Likelihood ratio analysi s showed that the biochemical markers with the highest positive likeli hood ratios for AMI during the first 2 hours following ED presentation were myoglobin and CK-MB. From 6 through 24 hours, the positive likel ihood ratios for cTn-I, CK-MB, and myoglobin were superior to those of CK and cTn-T Conclusions: cTn-I, CK-MB, and myoglobin are significant ly more specific for AMI than are CK and cTn-T Myoglobin is the bioche mical marker having the highest combination of sensitivity, specificit y, and negative predictive value for AMI within 2 hours of ED presenta tion. Neither cTn-I nor cTn-T offers significant advantages over myogl obin and CK-MB in the early (less than or equal to 2 hours) initial sc reening for AMI. The cardiac troponins are of benefit in identifying A MI greater than or equal to 6 hours after presentation.