Creatine kinase, total, serum or plasma (CK)
(age- and method-dependent)
Creatine kinase is an enzyme which catalyses the interconversion of creatine and phosphocreatine (PCr). Skeletal muscle, myocardium, and brain are rich in the enzyme.
CK is released when there is tissue damage (eg, myocardial infarction [MI], myopathy).
Increased in: MI, myocarditis, muscle trauma, rhabdomyolysis, muscular dystrophy, polymyositis, severe muscular exertion, malignant hyperthermia, hypothyroidism, cerebral infarction, surgery, Reye syndrome, tetanus, generalized convulsions, alcoholism, DC countershock. Drugs: clofibrate, HMG-CoA reductase inhibitors (statins).
CK is as sensitive a test as aldolase for muscle damage (eg, myositis), so aldolase is not needed for this condition. CK values may be increased up to 50-fold in active polymyositis and other inflammatory myopathies. A urine myoglobin may also be ordered for these conditions.
During an MI, serum CK level rises rapidly (within 3–5 hrs); elevation persists for 2–3 days post-MI. Total CK is not specific enough for use in diagnosis of MI, but a normal total CK has a high negative predictive value. A more specific test is needed for diagnosis of MI or acute coronary syndrome (eg, cardiac troponin I, which has largely replaced CK-MB).
Amato AA et al. Overview of the muscular dystrophies. Handb Clin Neurol 2011;101:1. [PMID: 21496621]
Milisenda JC et al. The diagnosis and classification of polymyositis. J Autoimmun 2014;48-49:118. [PMID: 24461380]
van der Kooi AJ et al. Idiopathic inflammatory myopathies. Handb Clin Neurol 2014;119:495. [PMID: 24365315]
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