Creatine kinase isoenzyme is a marker of myocardial injury. If elevated creatine kinase isoenzyme is found during laboratory tests, it indicates possible myocardial cell necrosis or myocardial cell injury. Unlike common creatine kinase, creatine kinase isoenzyme is specifically found in cardiac progenitor cells and is rarely found in skeletal muscle or smooth muscle, so damage to skeletal muscle or smooth muscle does not normally cause an increase in creatine kinase isoenzyme. In most cases, only ischemia, hypoxia, or necrosis of cardiac myocytes will lead to an increase in creatine kinase isoenzyme. In these cases, myocardial cells are necrotic and the creatine kinase isoenzyme is added to the bloodstream, which can be measured as an elevated value in laboratory tests.