Creatine kinase exists in 3 cytoplasmic forms: CK-MB (in cardiac muscle only), CK-MM (in striated and cardiac muscle) and CK BB (especially in brain).
Determination of CK in serum is used for the diagnosis and the follow-up of cardiac muscle damages. In myocardial infarction, the rates of total CK and CK-MB increase quickly until reaching a peak 10-24h after the onset of the infarction. The levels return to normal within 3 to 4 days.
CK-MB levels higher than normal can also be observed after muscle damages.