Creatine kinase (CK), also known as phosphocreatine kinase or creatine phosphokinase (CPK) is an enzyme () expressed by various tissue types. Its function is the catalysis of the conversion of creatine to phosphocreatine, consuming adenosine triphosphate (ATP) and generating adenosine diphosphate (ADP).

Types

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Every CK enzyme consists of two subunits, which can be either B (brain type) or M (muscle type). There are, therefore, three different isoenzymes: 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 those, there are two mitochondrial creatine kinases, the ubiquitous and sarcomeric form.

Isoenzyme patterns differ in tissues. CK-BB occurs mainly in tissues, and its levels do rarely have any significance in bloodstream. Muscle expresses CK-MM (98%) and CK-MB at low levels (1%) in muscle. The myocardium (heart muscle), in contrast, expresses CK-MM at 70% and CK-MB at 30%.

Uses

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CK is often determined routinely in emergency patients. In addition, it is determined specifically in patients with chest pain and acute renal failure. Normal values are usually between 25 and 200 U/L. This test is not specific for the type of CK that is elevated.

Elevation of CK is an indication of damage to muscle. It is therefore indicative of injury, rhabdomyolysis, myocardial infarction, myositis, myocarditis, malignant hyperthermia and neuroleptic malignant syndrome. It is also seen in McLeod syndrome.

Lowered CK can be an indication of alcoholic liver disease and rheumatoid arthritis.

Isoenzyme determination has been used extensively as an indication for myocardial damage in heart attacks. Troponin measurement has largely replaced this in many hospitals, although some centres still rely on CK-MB.

See also

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• Reference ranges for common blood tests

References

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• (CK-M chain) and (CK-B chain)
• Simply stated

Chemical pathology | EC 2.7.3 | Creatin-Kinase | Créatine kinase