To detect and monitor muscle damage and to help diagnose conditions associated with muscle damage
Creatine Kinase (CK) Test
If you have muscle pain, tenderness, weakness and swelling after muscle damage, particularly if your urine becomes dark reddish-brown in colour
A blood sample taken from a vein in the arm
This test measures the amount of creatine kinase (CK) in the blood. CK is an enzyme found in the heart, brain, skeletal muscle and other tissues. Increased amounts are released into the bloodstream when there is muscle damage. CK occurs in three major forms, called isoenzymes:
- CK-MB (found mostly in heart muscle)
- CK-BB (found mostly in brain)
- CK-MM (found in muscles)
How is the sample collected for testing?
A blood sample is taken by needle from the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is required.
How is it used?
The small amount of CK that is normally present in the blood comes primarily from skeletal muscles. Any condition that causes muscle damage and/or interferes with muscle energy production or use can cause an increase in CK. For example, inflammation of muscles, called myositis, can increase CK concentrations.
Rhabdomyolysis, a severe breakdown of skeletal muscle tissue that causes muscle pain, tenderness, weakness and swelling, is associated with significantly elevated levels of CK, often 100 times normal. Measurement of CK is used to assess the extent of muscle damage and to monitor its progress.
Measurement of CK is often used as part of the investigation of patients with suspected muscular dystrophy.
When is it requested?
Measurement of CK is requested in people who have sustained severe muscle trauma, particularly from crush injuries, burns or electrocution, and are likely to develop rhabdomyolysis.
CK may also be requested in those who develop symptoms or signs of rhabdomyolysis
- after being immobile for a long time on a hard surface, for example during an operation or after a stroke, drugs or alcohol
- following very severe exercise
- after a fit
- during a severe infection
- while taking certain medicines, for example a statin to lower cholesterol
Rhabdomyolysis is likely if the urine develops a reddish-brown colour and gives a positive dip-stick test for blood. (Myoglobin, a red protein released from damaged muscle, reacts with the dip-stick in the same way as haemoglobin from blood cells.) The excretion of myoglobin by the kidney can potentially cause kidney failure.
Blood concentrations of CK (or its CK-MM isoenzyme) are also requested as a first step in the diagnosis of muscular dystrophy in infants or children who
- have difficulty walking
- have difficulty standing
- have difficulty lifting weights
- need help climbing stairs
The test may subsequently be used to screen family members.
What does the test result mean?
A high CK concentration, or a result that goes up from the first to a second or later samples, generally indicates that there has been some recent muscle damage. Serial test results that peak and then begin to drop indicate that new muscle damage has diminished, while increasing and persistent elevations suggest continuing damage.
Is there anything else I should know?
Total CK is no longer requested in people with chest pain who are suspected of having had a heart attack. It was superseded first by one of its isoenzymes, CK-MB, which is more specific for heart muscle damage, and more recently by cardiac troponin. Troponin is highly specific, is more sensitive than CK-MB and remains raised much longer after a heart attack.
People who have greater muscle mass have higher normal CK levels. For example, a young fit male will have more muscle mass than an elderly female and hence a higher CK concentration. Normal exercise such as running or cycling and drug injections into muscle can increase CK concentrations.
How does the myoglobin that is released from muscle with CK during rhabdomyolysis produce renal failure?
Myoglobin released from damaged muscle into plasma is filtered by the kidneys into the urine but can precipitate in the kidney tubules, obstructing urine formation. This is a particular risk if shock lowers blood pressure and reduces the rate of urine production.
Are any other lab tests needed?
Yes, it is important to monitor the patient for increasing plasma potassium and decreasing plasma calcium levels.
Do all patients with muscular dystrophy have raised plasma CK values?
No, there are many different types of muscular dystrophy, some without raised CKs. However, if a patient and family members do have raised values, the CK test can avoid the need for muscle biopsy to carry out genetic tests.