View source for Creatine kinase

[[Image:Creatine Kinase.jpg|thumb|200px|Creatine Kinase]]
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==Overview==
'''Creatine kinase''' (CK), also known as '''phosphocreatine kinase''' or '''creatine phosphokinase''' (CPK) is an [[enzyme]] ({{EC number|2.7.3.2}}) expressed by various tissue types. It catalyses the conversion of [[creatine]] to [[phosphocreatine]], consuming [[adenosine triphosphate]] (ATP) and generating [[adenosine diphosphate]] (ADP).  

In tissues that consume ATP rapidly, especially [[skeletal muscle]], but also [[brain]] and [[smooth muscle]], phosphocreatine serves as an energy reservoir for the rapid regeneration of ATP. Thus Creatine Kinase is an important enzyme in such tissues.

Clinically, creatine kinase is assayed in blood tests as a marker of [[myocardial infarction]] (heart attack), [[rhabdomyolysis]] (severe muscle breakdown), [[muscular dystrophy]] and in [[acute renal failure]].

There are three different isoenzymes that come from three distinct locations in the body:
* '''BB''': Brain, prostate, gastrointestinal, breast, ovary, lung
* '''MM''': Skeletal muscle
* '''MB''': Heart

==Types==
In most of the [[Cell (biology)|cell]], the CK enzyme consists of two subunits, which can be either ''B'' (brain type) or ''M'' (muscle type). There are, therefore, three different [[isoenzyme]]s: CK-MM, CK-BB and CK-MB. The genes for these subunits are located on different [[chromosome]]s: ''B'' on 14q32 and ''M'' on 19q13. In addition to those, there are two [[mitochondrium|mitochondrial]] creatine kinases, the ''ubiquitous'' and ''sarcomeric'' form.
{{protein
| Name = creatine kinase, brain
| caption = 
| image = 
| width = 
| HGNCid = 1991
| Symbol = CKB
| AltSymbols = CKBB, CK-1
| EntrezGene = 1152
| OMIM = 123280
| RefSeq = NM_001823
| UniProt = P12277
| PDB = 
| ECnumber = 2.7.3.2
| Chromosome = 14
| Arm = q
| Band = 32.3
| LocusSupplementaryData = 
}}
{{protein
| Name = creatine kinase, muscle
| caption = 
| image = creatine kinase.PNG
| width = 
| HGNCid = 1994
| Symbol = CKM
| AltSymbols = CKMM, CK-3
| EntrezGene = 1158
| OMIM = 123310
| RefSeq = NM_001824
| UniProt = P06732
| PDB = 
| ECnumber = 2.7.3.2
| Chromosome = 19
| Arm = q
| Band = 13.2
| LocusSupplementaryData = -13.3
}}
{{Protbox finish}} 

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Isoenzyme patterns differ in tissues. CK-BB occurs mainly in tissues, and its levels do rarely have any significance in bloodstream. Skeletal muscle expresses CK-MM (98%) and low levels of CK-MB (1%). The [[myocardium]] (heart muscle), in contrast, expresses CK-MM at 70% and CK-MB at 25-30%. CK-BB is expressed in all tissues at low levels and has little clinical relevance.

The mitochondrial creatine kinase (CK<sub>m</sub>), which produces ATP from ADP by converting creatine phosphate to creatine, is present between the two membranes of the mitochondrion. Apart from the mitochondrial form, there are three forms present in the cytosol—CK<sub>a</sub> (in times of acute need, produces ATP in the cytosol at the cost of creatine phosphate), CK<sub>c</sub> (maintains critical concentration of creatine and creatine phosphate in the cytosol by coupling their phosphorylation and dephosphorylation respectively with ATP and ADP) and CK<sub>g</sub> (which couples direct phosphorylation of creatine to the glycolytic pathway (see [[glycolysis]]).

==Laboratory testing==
CK is often determined routinely in emergency patients. In addition, it is determined specifically in patients with [[chest pain]] and [[acute renal failure]] is suspected. Normal values are usually between 25 and 200 U/[[litre|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]], [[muscular dystrophy]], [[myositis]], [[myocarditis]], [[malignant hyperthermia]] and [[neuroleptic malignant syndrome]]. It is also seen in [[McLeod syndrome]] and [[hypothyroidism]]. The use of [[statin]] medications, which are commonly used to decrease serum cholesterol levels, may be associated with elevation of the CPK level in about 1% of the patients taking these medications, and with actual muscle damage in a much smaller proportion.

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 centers still rely on CK-MB.

== Differential Diagnosis ==
=== Differential Diagnosis of Increased Total CK ===
* [[Alcoholism]]
* Arterial [[embolism]]
* Bacterial [[myositis]]
* [[Becker's Muscular Dystrophy]]
* Crush injury or [[trauma]]
* [[Duchenne's Muscular Dystrophy]]
* [[Hyperthermia]]
* [[Hyperthyroidism]]
* [[Hypothyroidism]]
* [[Intramuscular injection]]s
* [[Lymphangitis]]
* [[Leyden-Moebius Muscular Dystrophy]]
* [[Liver]], [[pancreas]] and gastrointestinal diseases
* Medications such as [[Saxagliptin]]
* Muscular [[spasm]]
* [[Myasthenia Gravis]]
* [[Myositis]]
* Neurogenic muscular atrophy
* [[Pancreatic cancer]]
* [[Polymyositis]]
*[[Pralidoxime]]
* [[Pregnancy]] and labor
* [[Rhabdomyolysis]]
* [[Seizure]]
* Surgery
* [[Thyrotoxicosis]]
* Vigorous exercise
* [[Viral myositis]]

==Differential Diagnosis of Increased Total CK and CK-MB Ratio==
* [[Cardiac contusion]]
* [[Cardiogenic shock]]
* [[Heart surgery]]
* [[Myocardial Infarction]]
* [[Perimyocarditis]]
* [[Right ventricular failure]]

==See also==
* [[reference ranges for common blood tests]]
* [[kinase]]

==References==
* [http://www.mdausa.org/publications/Quest/q71ss-cktest.html Simply stated at mdausa.org]
* {{MeshName|Creatine+Kinase}}

{{Kinases}}
{{Mitochondrial enzymes}}


[[Category:Chemical pathology]]
[[Category:EC 2.7.3]]

[[Category:Cardiology]]

[[de:Creatin-Kinase]]
[[es:Creatina quinasa]]
[[fr:Créatine kinase]]
[[it:Creatinchinasi]]
[[ja:クレアチンキナーゼ]]
[[pl:Kinaza kreatynowa]]

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