Serum Creatine Phosphokinase (CPK) Activity in Disorders of Heart and Skeletal Muscle

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Abstract
A clinical and laboratory study of serum creatine phosphokinase (CPK) activity was undertaken to assess its usefulness and reliability as a laboratory aid in clinical medicine. Several important considerations in laboratory technique are discussed. High CPK values were found in patients with Duchenne type muscular dystrophy (MD), polymyositis and acute myocardial infarction. Small to moderate elevations were noted in adult types of MD, female relatives of some paitents with MD, and in. some patients with coronary insufficiency. Patients with acute and chronic liver disease, renal infarction, stabilized chronic renal disease, hemolytic anemia, pulmonary embolism, solid tumors and leukemia had normal serum CPK. In human and canine tissue homo-genates, highest CPK activity was found in skeletal muscle and heart, followed in order of decreasing activity by brain and smooth muscle organs. Liver, kidney, lung, prostate, pancreas and human RBC''s had negligible CPK activity. Intramuscular drug injections, muscle trauma and strenuous exercise may produce transient elevations of serum CPK and other enzymes. If serum CPK is to be determined and drugs must be given parenterally, subcutaneous or intravenous routes should be used if possible. For laboratory confirmation of active myocardial or skeletal muscle disease, serum CPK is more sensitive and specific than LDH (lactic dehydrogenase) or GOT (glutamic oxaloacetic transamin-ase). It can be particularly valuable in patients with hepatocellular damage, pulmonary embolism, hemolytic states, or other conditions which may cause elevation of LDH, GOT, and other ubiquitous enzymes. It is concluded that when used intelligently, serum CPK can be a useful laboratory aid in clinical medicine.