EVIDENCE-BASED ANSWER:
Measurement of troponin levels provides the most sensitive and accurate serologic information in evaluating a patient with acute coronary syndrome (ACS); troponin elevations are more sensitive than elevations of creatine kinase-MB (CK-MB). Isolated elevation of troponin levels increases the likelihood of myocardial infarction (MI) or death, whereas isolated elevation of CK-MB levels doesn’t. (Strength of recommendation [SOR] for all statements: A, multiple, large prospective cohort studies.)
Repeated measurement of troponin levels at presentation and then 3 and 6 hours afterward increases the diagnostic sensitivity for acute myocardial infarction (AMI) (SOR: A, multiple, small prospective studies).
EVIDENCE SUMMARY
Troponin I and T proteins are specific to cardiac myocytes and, unlike CK-MB, aren’t elevated by damage to skeletal muscle.
Measuring troponin levels increased the number of patients diagnosed with AMI
A multinational prospective cohort study of patients with suspected ACS (N=10,719) found that measuring troponin levels in addition to CK-MB levels improved the diagnosis of AMI.1 Investigators used elevation of any biomarker (CK, CK-MB, or troponin I or T) above the upper limit of normal as their diagnostic criterion. They found that measuring troponin increased the number of patients diagnosed with AMI by 10.4% over patients diagnosed using CK and CK-MB levels. Elevated troponin levels were associated with an inpatient mortality rate 1.5 to 3 times higher, regardless of the patient’s CK-MB status.
Troponin levels are more sensitive and specific than CK-MB
A prospective cohort study of 718 patients with suspected AMI calculated the area under curve (AUC) of the receiver operator curve—a measure of diagnostic accuracy in which an AUC value of 1 indicates 100% sensitivity and specificity—for troponin and CK-MB levels at initial presentation.2 Two independent cardiologists reviewed all available medical records and made the final diagnosis. The AUCs for troponin levels ranged from 0.94 to 0.96 compared with 0.88 for CK-MB.