Creatine kinase (CK), formerly known as creatine phosphokinase, is an intracellular enzyme present in greatest amounts in skeletal muscle, myocardium, and brain; smaller amounts occur in other visceral tissues.
Disruption of cell membranes due to hypoxia or other injury releases CK from the cellular cytosol into the systemic circulation. On this basis, elevated serum levels of CK have been used as a sensitive but nonspecific test for myocardial infarction. The poor specificity reflects the ubiquity of CK in many tissues other than the myocardium.
Because of the many current assay methods in use, there is no standard reference value for serum CK. Normal values are best determined locally based on the method employed and the ranges for healthy controls. Values are expressed in international units per liter.
CK is a dimeric molecule composed of two subunits designated M and B. Combinations of these subunits form the isoenzymes CK–MM, CK–MB, and CK–BB. A significant concentration of CK–MB isoenzyme is found almost exclusively in the myocardium, and the appearance of elevated CK–MB levels in serum is highly specific and sensitive for myocardial cell wall injury. Normal reference values for serum CK–MB range from 3 to 5% (percentage of total CK) or 5 to 25 IU/L.
Copyright © 1990, Butterworth Publishers, a division of Reed Publishing.