Test for acute myocardial infarct and for skeletal muscular damage; elevated in some patients with myxedema (hypothyroidism), malignant hyperthermia syndrome, and muscular dystrophy. CK is a marker for Duchenne muscular dystrophy, with elevations of 20 to 200 times normal.1 CK is increased in female carriers of this X-linked disease, and in muscular stress, in polymyositis, dermatomyositis, and with muscle trauma. Elevated in myocarditis. Documentation of postictal state (recent grand mal seizure). Extremely high values are seen in some instances of myositis and in the postictal state. CK may be elevated in a number of entities, including the eosinophilia-myalgia syndrome.2 Marked increases occur with rhabdomyolysis including that with cocaine intoxication.3 CK is sometimes increased with cerebrovascular accident. Malignancy (advanced) may show increased CK.4 Cardioversion with multiple shocks may release CK-MB and may result in a false-positive diagnosis of myocardial infarction.5 Low CK may reflect decreased muscle mass. It has been reported with a number of entities, including metastatic neoplasia, patients with steroid therapy, with alcoholic liver disease6 and with connective tissue diseases.7 Overnight bedrest may lower CK 10% to 20%.