CPK

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Introductions

Creatine phosphokinase (CPK) is abundant in skeletal muscle, cardiac muscle, and smooth muscle, followed by brain tissue, and to a lesser extent in the gastrointestinal tract, lung, and kidney. Creatine kinase is mainly found in the cytoplasm and mitochondria and is an important kinase directly related to intracellular energy functioning, muscle contraction, and ATP regeneration. Measurement of creatine kinase activity can be used for the diagnosis of skeletal muscle disease and cardiac muscle disease. In the hospital, when a person shows signs of a heart attack, his or her CK-MB level is usually checked. However, in lupus treatment, an elevated CPK may indicate muscle inflammation due to disease activity or overlapping conditions. CPK levels may also be high after strenuous exercise, so your doctor may want to recheck your CPK after a few days of rest.

Classifications

In cells, the cytosolic CK enzyme consists of two subunits, either B (brain type) or M (muscle type). Thus, three different isoforms exist: CK-MM, CK-BB and CK-MB. The genes for these subunits are located on different chromosomes: B on 14q32 and M on 19q13. In addition to these three cytosolic CK isoforms, there are two other mitochondrial creatine kinase isoforms, the ubiquitous and the myosin form. The functional entity of the mitochondrial CK isoform is composed of four octamers of each dimer.

Functions

CPK enhances the contractility of skeletal muscle, heart and smooth muscle and is involved in the production of blood pressure. In addition, ADP scavenging by creatine kinase is associated with bleeding disorders: individuals with highly elevated plasma CK may be prone to hemorrhage. The bound cytosolic CK accepts PCr across the cell and uses ADP to regenerate ATP, which can then be used by ATP as a source of energy (CK is closely related to ATPase, forming functionally coupled micro compartments).

High CPK levels may be seen in people who have:

• Brain injury or stroke
• Convulsions
• Delirium tremens
• Dermatomyositis or polymyositis
• Electric shock
• Heart attack
• Inflammation of the heart muscle (myocarditis)
• Lung tissue death (pulmonary infarction)
• Muscular dystrophies
• Myopathy
• Rhabdomyolysis
• Trauma

Application for CPK Test

• Diagnose heart attack
• Evaluate cause of chest pain
• Determine if or how badly a muscle is damaged
• Detect dermatomyositis, polymyositis, and other muscle diseases
• Tell the difference between malignant hyperthermia and postoperative infection

Clinical Significance

• Exercise can lead to a significant increase in creatine kinase, and the more vigorous and prolonged the exercise, the more pronounced the increase in creatine kinase.
• Higher than normal serum creatine kinase activity in childbirth and newborns.
• Some therapeutic and diagnostic measures, such as installation of artificial pacemakers, electroshock, radiation therapy, cardiac compression, cardiac catheterization, and urinary tract examination, can increase serum creatine kinase activity.
• Men with high muscle volume have higher serum creatine kinase activity than women.
• Intramuscular injection of certain drugs (such as anesthetics, painkillers, antibiotics, dexamethasone, etc.) can lead to increased serum creatine kinase activity.
• Oral administration of certain drugs, such as clofibrate, can increase serum creatine kinase activity.
• Pathological increase: myocardial infarction, viral myocarditis, dermatomyositis, myotonic dystrophy, pericarditis, cerebrovascular accident, etc.