Creatine kinase (CK, phosphocreatine kinase, creatine phosphokinase, CPK) is an enzyme. It is made up of 2 subunits:
- M subunit coded for on chromosome 19q13
- B subunit coded for on chromosome 14q32
The common isoenzymes in man are therefore CK-MM, CK-BB and CK-MB although there are two separate mitochrondial creatine kinase's. As the CK-MB is about 30% of the myocardiums CK and only 1% of sketeletal muscle this isoenzyme had a brief period as the most specific routinely measured marker of myocardial damage. It has now been replaced by the usually more expensive but specific troponin assays in ischaemic heart disease presentations as levels are better related to prognosis.
It is used as a marker of muscle damage. As routine measuring its level in the blood has been largely replaced, no longer do we have the doctor in training asking why the CK is grossly raised in a patient with abdominal pain and shock when ECG shows no evidence of myocardial ischaemia (bowel ischaemia), the mildly raised CK that is due to a patients genetic inheritance no longer significantly adds to consultant physician workload, and no longer the diagnosis of Neuroleptic malignant syndrome suddenly clicks in house staff because someone ordered routine bloods in A&E.