Troponin T or troponin I or CK-MB (or none?)

Differential diagnosis of patients who present with chest pain remains problematical. It has been shown that 11.8-7% of patients with acute myocardial infarction (AMI) are sent home from the emergency department (ED). Audit of our own ED has shown the incidence of missed prognostically significant myocardial damage to be 6.7%. Diagnostic criteria for AMI have classically been based on the triad of history, ECG and measurement of cardiac enzymes. The choice of 'cardiac enzymes' has been dictated by the evolution of laboratory techniques, commencing with measurement of aspartate transaminase and progressing to measurement of creatine kinase (CK) and its MB isoenzyme (CK-MB). Measurement of CK-MB has been shown by both clinical studies and rigorous statistical analysis to represent the best test for the diagnosis of AMI. The advent of real time immunoassay together with advances in therapeutic options for management of acute coronary syndromes (ACS) has resulted in a paradigm shift in the approach to laboratory testing. Immunoassay for CK-MB (CK-MB mass measurement) is diagnostically superior to CK-MB activity measurement and is the test of choice for 'classical' AMI. Development of immunoassays for the cardiac troponins, i.e. cardiac troponin T (cTnT) and cardiac troponin I (cTnI), has enhanced diagnostic specificity. These measurements are completely specific for cardiac damage, allow quantitation of the extent of infarction and are diagnostically superior to CK-MB measurement. Applications of this specificity have included the differential diagnosis of CK elevation in arduous physical training, detection of myocardial damage after DC cardioversion and prediction of ejection fraction. Of more interest is the utility of these markers in management of patients presenting without clear electrocardiographic changes. Diagnosis and management of patients presenting with ST segment elevation has been clarified by large clinical trials of thrombolytic agents. In such patients, thrombolysis is the treatment of choice. Patients presenting with ST segment elevation represents the minority of patients with probable ACS 9.6% of all patients presenting to our hospital. The majority require risk stratification into high- and low-risk groups. It is here that cardiac troponins have a major role. The measurement of cTnT has been shown in a large number of studies to enable risk stratification of patients with unstable angina. The combination of cTnT, admission ECG and stress ECG can be used for a comprehensive risk stratification of patients with unstable angina. The combination of cTnT, admission ECG and stress ECG can be used for a comprehensive risk stratification which can be completed by 24 h from admission, as well as allowing a safe discharge policy from the ED. Measurements of cardiac troponins can also be used to predict prognosis in patients with other diagnostic categories. Patients with cardiac failure can be risk stratified according to cTnT status. cTnT status on admission allows subdivision into high- and low-risk groups in patients presenting with ST segment elevation. Certainly, cTnT measurement can be incorporated into a clinical decision-making strategy to assign patients to investigation and management pathways. There is evidence that cTnT may be useful to guide therapeutic options. The major issue is one of cost. In the U.K. model of managed care with undemanding diagnostic standards, the role of cTnT will be to enhance clinical decision-making strategies, to provide accurate diagnosis and to reduce lengths of stay. This can be shown to have potential for major improvements in cost efficiency. Improvements in diagnostic accuracy can reduce inappropriate long-term drug therapy. In systems with a more aggressive laboratory investigation strategy, rationalization of test numbers will provide an immediate cost reduction while improving quality. Finally, use of point-of-care testing (POCT) means that biochemical testing can be pe