Serum creatine kinase in the diagnosis of acute myocardial infarction. Optimal sampling frequency.

To document optimal sampling frequency, we reviewed creatine kinase (CK) myocardial specific isoenzyme (CKMB) results in 314 patients with suspected acute myocardial infarction (MI). In 127 patients with elevated CK/CKMB, peak CK observed using all samples (every four-hour [Q4hr] method) was compared with results that would have been obtained had samples been taken on admission and either twice daily (every 12-hour [Q12hr] method) or once daily (every 24-hour [Q24hr] method). Although average peak CK was statistically different (Q4hr greater than Q12hr greater than Q24hr), major underestimation of peak CK (greater than or equal to 500 units/L) was uncommon (3%) using the Q12hr method, suggesting that Q12hr sampling is a practical, cost-effective approach for patients with suspected acute MI.