Objective: The aim of the study was to investigate the clinical performance of serum creatine kinase (CK), CKMB (mass and activity), Troponin T (TnT) and Troponin I (TnI) in the diagnosis of acute myocardial infarction (AMI) in patients admitted to the Coronary Care Unit at Tan Tock Seng Hospital between June and July 1998.
Methods: Routine blood samples sent to the laboratory for cardiac enzyme determination (CK, CKMB activity) were stored at -20 degrees C for later determination of CKMB mass (Abbott Axsym, Ortho Clinical Diagnostics (OCD) ECi and Roche Elecsys), Troponin I (Abbott Axsym) and Troponin T (Roche Elecsys). For CKMB mass measurements, the relative index (RI = CKMB mass/CK) was calculated. The diagnosis of acute myocardial infarction was obtained from inspection of clinical notes and/or discharge diagnosis for each patient.
Results: Forty-four of fifty-nine specimens were from AMI patients. Area under Receiver Operating Curve values were: CK 0.56, CKMB activity 0.72, percentage of CKMB activity 0.73, CKMB mass (Abbott) 0.76, CKMB mass (Roche) 0.77, CKMB mass (OCD) 0.78, RI (Roche) 0.83, RI (Abbott) 0.86, RI (OCD) 0.87, TnT 0.94, TnI 0.95. Sensitivity: TnI 88%, TnT 93%; specificity TnI 100%, TnT 92%. There was no significant difference in performance between Troponin T and Troponin I assays or between any of the CKMB mass measurements.
Conclusion: Troponin T and I are superior to CKMB (mass or activity) and CK in the identification of patients with AMI. Combining multiple sampling of the percentage of CKMB with single confirmatory troponin testing may provide a cost-effective testing protocol for suspected AMI patients.