- creatine kinase dimer of M and B chains
- found in myocardial cytosol (also in skeletal muscle)
- rises within 4-12 hours pos infarction (high sensitivity and specificity)
- peaks at 18-24 hrs
- returns to baseline by 40 hours
- diagnosis of MI can be enhanced by looking at MB isoforms or using MB fraction of total CK (important if there is significant skeletal muscle damage, cardioversion, hypothyroidism, renal failure)
- no increase in myocarditis
- rapid return to normal level allows for potential diagnosis of re-infarction.