Context: Controversy surrounds the diagnostic and prognostic importance of slightly elevated cardiac markers in patients with acute coronary syndromes without ST-segment elevation.
Objectives: To investigate the relationship between peak creatine kinase (CK)-MB level and outcome and to determine whether a threshold CK-MB level exists below which risk is not increased.
Design and setting: Retrospective observational analysis of data from the international Platelet Glycoprotein IIb/IIIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy (PURSUIT) trial, conducted from November 1995 to January 1997.
Patients: A total of 8250 patients with acute coronary syndromes without ST-segment elevation who had at least 1 CK-MB sample collected during their index hospitalization.
Main outcome measure: Mortality at 30 days and 6 months, was assessed by category of index-hospitalization peak CK-MB level (0-1, >1-2, >2-3, >3-5, >5-10, or >10 times the upper limit of normal). Multivariable logistic regression was used to determine the independent prognostic significance of peak CK-MB level after adjustment for baseline predictors of 30-day and 6-month mortality.
Results: Mortality at 30 days and 6 months increased from 1.8% and 4.0%, respectively, in patients with normal peak CK-MB levels, to 3.3% and 6.2 % at peak CK-MB levels 1 to 2 times normal, to 5.1% and 7.5% at peak CK-MB levels 3 to 5 times normal, and to 8.3% and 11.0% at peak CK-MB levels greater than 10 times normal. Log-transformed peak CK-MB levels were predictive of adjusted 30-day and 6-month mortality (P<.001 for both).
Conclusions: Our data show that elevation of CK-MB level is strongly related to mortality in patients with acute coronary syndromes without ST-segment elevation, and that the increased risk begins with CK-MB levels just above normal. In the appropriate clinical context, even minor CK-MB elevations should be considered indicative of myocardial infarction.