Dr Graham Jones
Department of Chemical Pathology

Creatine Kinase (CK) is an enzyme found in myocytes which catalyses the transfer of high energy phosphate groups from creatine phosphate to ADP in order to produce ATP. The enzyme is a dimer with two subunits which may be of the M or B type making three common isoforms: CK-MM, CK-MB and CK-BB. The molecular weight is about 50,000 dalton and the Enzyme Commision number is EC 2.7.3.2.

Pathology     

Causes of Elevated serum CK

Any cause of muscle damage, skelatal, cardiac or other.

Skeletal Muscle Damage
Largely CK-MM. Serum cardiac -specific troponin not elevated.

• Trauma (eg MVA, surgery)
• Rhabdomyolysis (may reach very high levels, up to over 100,000 U/L)
• Myositis (Note: CK not elevated in neurogenic myopathy, eg MS)
• Muscular dystrophy
• Hypothyroidism
• Convulsions
• Hyper / hypothermia
• Dermatomyositis
• Injections (up to 2 - 4 x upper limit of normal)
• Drugs: lignocaine, digoxin
• Cardioversion

Cardiac Muscle Damage
5 - 15% CK-MB. Cardiac troponin usually elevated.

• Acute myocardial infarction
• Myocarditis / pericarditis
• Trauma (cardiac compression, cardiac surgery)
• Multi-organ failure
• Cardiac arrest

Other

• Stroke
• Neonates
• Some malignancies (prostate, large bowel)
• Macro-CK

Measurement

The sample requirement for measurement of serum CK is either a serum (gold-top) or heparin (lime-top) tube. Lime top is preferred for inpatients. The assay is available 7 days / 24 hours and results are available within 2 hours of sample delivery to the laboratory.

Reference Interval

The Upper limit of the SydPath Reference interval is 130 U/L for males and 110 U/L for females.. Note that the distribution in a healthy population is severely skewed with a long tail to the right, thus some results in healthy people may be a significant margin above the upper reference limit. Higher levels are commonly found in black Americans compared to Caucasians.