Creatine kinase

Last revised by Yuranga Weerakkody on 19 Jun 2019

Creatine kinase (CK), also known as creatine phosphokinase (CPK), is a key enzyme, for energy production in mitochondria and muscle tissues. It is important as a diagnostic assay in clinical practice, primarily because inflamed/injured muscle releases creatine kinase into the circulation 1.


Creatine kinase is an enzyme that catalyzes the transfer of a phosphate group from creatine phosphate to adenosine diphosphate to form adenosine triphosphate (ATP). It is predominantly located within mitochondria, the cytoplasm of myocytes and in myofibrils 2. A constant supply of ATP is critical for muscular activity during exercise.

Creatine kinase is a dimeric molecule, with three main isoforms:

  • CK-MM: more than 99% of the CK in skeletal muscle
  • CK-MB: predominant form of CK in cardiac muscle
  • CK-BB

Elevated creatine kinase

There are a very large number of causes of an increased serum creatine kinase:

Electrolyte disturbances
  • hyponatremia
  • hypokalemia
  • hypophosphatemia
Muscle injury
  • vigorous exercise
  • intramuscular injections
  • seizures
  • needle electromyography
  • statins
  • fibrates
  • antiretrovirals
  • beta-blockers
  • clozapine
  • angiotensin II receptor blockers
  • hydroxychloroquine
  • isotretinoin
  • colchicine

Many of these are rare/very rare

Muscle dystrophies
Metabolic and mitochondrial disorders of muscle
Inflammatory myopathies
Miscellaneous neuromuscular disorders
  • celiac disease
  • malignancy
  • macroenzyme CK
  • surgery
  • pregnancy
  • cardiac disease
  • acute kidney disease
  • viral illness

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