CK-MB test explained

Creatine kinase (CK, sometimes called creatine phosphokinase, CPK) is an enzyme involved in the energy metabolism of cells — it is found mostly in muscles, the heart and the brain. CK is made up of isoforms (isoenzymes) that show which tissue the enzyme came from: CK-MM is characteristic of skeletal muscle, CK-BB of the brain and smooth muscle, and CK-MB is found mostly in heart muscle. When heart muscle cells are damaged — for example by a myocardial infarction or inflammation — they release enzymes into the blood, CK-MB among them, so the amount of this fraction in blood rises. The CK-MB test was historically used to detect heart muscle damage and to assess its size, but over recent decades it has largely been replaced by the more sensitive and more specific troponin test. Even so, CK-MB is sometimes tested in addition, when a doctor needs to assess whether a rise is related to heart muscle — according to MedlinePlus, a high amount of CK-MB most often indicates heart muscle damage, while a high amount of CK-MM most often indicates skeletal muscle damage.

• When there is chest pain or pressure and heart muscle damage is suspected
• When it needs to be established whether a raised total creatine kinase is related to the heart or to skeletal muscle (MedlinePlus)
• Together with total creatine kinase (CK) and troponin, to clarify whether a raised CK value is related to the heart or to skeletal muscle
• To monitor the size of heart muscle damage in hospital after an acute event

How to prepare

• No special preparation is usually needed — see also how to prepare for a blood test
• It is worth telling your doctor about the medicines you take (for example medicines that lower cholesterol) and about any recent intense physical exertion or injury, because these can temporarily affect the total amount of creatine kinase

Reference range

No single figure for CK-MB is given here. According to MedlinePlus, a normal creatine kinase value depends on age, sex, race, muscle mass and physical activity, and the CK-MB share rises when heart muscle cells are damaged, for example after a heart attack. So a CK-MB result is not compared with one universal number: it is assessed together with total creatine kinase, troponin and the clinical picture, and only a doctor can say what it means in an individual case.

A raised CK-MB

A raised CK-MB is most often linked to heart muscle damage — a myocardial infarction or inflammation of the heart muscle (myocarditis). Because a share of CK-MB is also present in skeletal muscle, the amount can also rise because of muscle damage, so the result is always assessed together with troponin and the clinical picture.

What can raise CK-MB

• Myocardial infarction (heart attack) or other acute heart muscle damage
• Inflammation of the heart muscle (myocarditis)
• Skeletal muscle damage, related to total creatine kinase — injury, intense physical exertion, muscle diseases
• Some medicines that affect cholesterol metabolism can raise the total amount of creatine kinase

What to discuss with a doctor

• The result is always assessed together with troponin and clinical symptoms, because CK-MB by itself is not the most accurate marker of heart damage
• Total creatine kinase (CK) — helps distinguish whether the rise is related to the heart or to skeletal muscle
• Whether there has been recent intense physical exertion, injury or muscle disease
• Repeat testing over time — the amount of CK-MB changes faster after heart damage than the amount of troponin

What a single result does not tell you

A CK-MB result on its own is not a diagnosis. The value is assessed together with other tests (troponin, total CK), with symptoms and with a doctor's examination — only a doctor can explain what the result means in a particular case. On reading laboratory results in general, see how to read blood test results.