Comparison of CK-MB subforms and troponin I in the evaluation of patients with acute coronary syndromes

Background: Among the various markers of myocardial injury, CK-MB subforms MB2, MB1 and their ratio (CKMBS) have been reported to be the most sensitive early marker of acute myocardial infarction. Hypothesis: The aim of this study was to determine if CKMBS is superior to troponin I in the prediction of major cardiac events in patients with acute coronary syndromes. Methods: The prognostic values of CKMBS and troponin I were compared in 100 consecutive patients with acute coronary syndromes. CKMBS and troponin I were measured on arrival to the emergency room and if the duration of chest pain was < 8 hours, a second measurement was done 8 hours later. In addition, CK-MB was measured every 8 hours for 24 hours. Physicians were blinded to the Troponin I data. Patients were followed until their discharge from the hospital for the occurrence of major cardiac events (myocardial infarction, coronary angioplasty, coronary bypass surgery, or death). Results: Major cardiac events occurred in 24 patients. The sensitivities of CK-MB, CKMBS, and troponin I in the prediction of major cardiac events were 58%, 62%, and 87%, and specificities were 88%, 73%, and 88%, respectively. By multiple logistic regression analysis, troponin I (chisquared 26.2, odds ratio 54.9) and CKMBS (chi-squared 6.4, odds ratio 6.59) wereindependent predictors of major cardiac events. In the whole group, troponin I was better than CKMBS in the prediction of the occurrence or absence of cardiac events (88% versus 73%, P =.009, odds ratio 2.67 ± 1.48). In the 77 patients with normal CK-MB, there were 9 with elevated troponin I and 21 with elevated CKMBS. Among these 77 patients, troponin I was better than CKMBS in the prediction of the occurrence or absence of cardiac events (72% versus 57%, P =.0027, odds ratio 4.0 ± 1.65). However, among the 23 patients with elevated CK-MB, troponin was not better than CKMBS. There was a significant increase in the incidence of cardiac events with increasing levels of troponin I (chi-squared 49.79, P <.0001). Conclusions: For the prediction of major cardiac events in acute coronary syndromes, troponin I is superior to CKMBS, especially in patients with normal CK-MB.