Creatine kinase MB, also known as creatine kinase isoenzyme and abbreviated as CK-MB, can be elevated for a variety of clinical reasons, such as hypothyroidism, myocardial injury, myocarditis, and myocardial infarction. However, creatine kinase isoenzyme is relatively more specific for myocardial injury and necrosis, and if a patient has a doubled increase in creatine kinase, acute myocardial infarction or myocarditis is highly considered. If creatine kinase isoenzyme alone is elevated but creatine kinase is normal, consider the possibility that patients with laboratory errors or tumors are prone to this abnormality. Because creatine kinase includes creatine kinase isozymes, it is not possible in practice to simply have an elevated creatine kinase isoenzyme but a normal creatine kinase.