Creatine kinase (CK) test: what the result means

Creatine kinase (CK), also called creatine phosphokinase (CPK), is an enzyme that helps cells produce energy. The largest amounts are in skeletal muscle and heart muscle, smaller amounts in the brain. While muscle cells are healthy, CK stays inside them; when muscle or heart tissue is damaged, CK enters the blood and the amount in blood rises. That is why a CK test is used when muscle damage, muscle diseases or a heart attack is suspected. Sometimes the CK isoenzyme fractions (CK-MB) are tested as well, so that it can be distinguished more precisely whether the rise comes from the heart or from skeletal muscle. The CK level depends on age, sex, race, muscle mass and physical activity, so there is no single universal figure that fits everyone — the result is always assessed together with symptoms and other tests.

• When there is muscle pain, muscle cramps or spasms
• When there is muscle weakness, impaired balance or frequent falls
• When numbness, tingling, swollen legs or feet, or darkened urine appear
• When a heart attack is suspected, or the cause of chest pain is being clarified
• To monitor a known muscle disease (for example muscular dystrophy or myositis) or the course of its treatment
• After intense physical exertion or an injury, when muscle damage is suspected

According to MedlinePlus, a raised CK is considered a sign of damage to muscle, heart or brain tissue. The most common causes are intense physical exertion, an injury, a heart attack or myocarditis, a stroke, muscle diseases and rhabdomyolysis. To establish the cause, troponin and the CK-MB fraction are often assessed alongside it.

What can raise CK

• Skeletal muscle damage — an injury, a disease, intense physical exertion
• Heart muscle damage — a heart attack or myocarditis
• A stroke or brain damage
• Rhabdomyolysis (sudden breakdown of muscle tissue)
• Muscular dystrophies or myositis

Symptoms linked to a raised CK

MedlinePlus notes that the following are often linked to the muscle damage that can raise CK:

• Muscle pain and/or cramps
• Muscle weakness
• Balance problems and/or frequent falls
• Numbness or tingling
• Darkened urine
• Swollen legs or feet

What to discuss with a doctor

• Whether there was any recent heavy physical exertion or injury around the time of the test
• Troponin and CK-MB tests, if heart damage is suspected
• A review of the medicines you take with your doctor — some medicines can temporarily raise CK
• When to repeat the test, so that the change over time can be seen

What a single result does not tell you

There is no single universal CK figure that fits everyone: the level depends on age, sex, race, muscle mass and physical activity, so the result is always assessed together with symptoms and other tests. The exact reference range also depends on the method your laboratory uses, so compare your value with the range printed on your own report — on reading laboratory results in general, see how to read blood test results.

Related tests

• Troponin
• CK-MB
• LDH
• Creatinine
• Potassium