Creatine kinase

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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 .

Physiology

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 . 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:

Endocrine

hypothyroidism (hyperthyroidism: usually normal CK, but rarely raised)
hyperparathyroidism
acromegaly
Cushing syndrome

Electrolyte disturbances

hyponatremia
hypokalemia
hypophosphatemia

Muscle injury

vigorous exercise
intramuscular injections
seizures
needle electromyography

Drugs

statins
fibrates
antiretrovirals
beta-blockers
clozapine
angiotensin II receptor blockers
hydroxychloroquine
isotretinoin
colchicine

Neuromuscular

Many of these are rare/very rare

Muscle dystrophies

muscular dystrophies
- Duchenne
- Becker
- dystrophin mutations in female carriers
limb girdle muscle dystrophy
myofibrillar myopathy
desmin-related myofibrillar myopathy
myotonic dystrophy

Metabolic and mitochondrial disorders of muscle

carnitine palmitoyltransferase II deficiency
McArdle disease
myoadenylate deaminase deficiency
mitochondrial myopathies
Pompe disease

Inflammatory myopathies

Miscellaneous neuromuscular disorders

Miscellaneous

celiac disease
malignancy
macroenzyme CK
surgery
pregnancy
cardiac disease
acute kidney disease
viral illness