CK (Creatine Kinase) and CK-MB
Definition
CK is an enzyme that helps produce energy in the body. Most of it is found in skeletal muscle, with smaller amounts in heart and brain tissue. Normally, a small amount of CK enters the blood from the ordinary wear and tear of muscles.
It has three isoenzymes:
| Isoenzyme | What it indicates |
|---|---|
| CK-MM | Skeletal muscle damage, from disease, injury, medications or intense exercise |
| CK-MB | Heart muscle damage, typically a heart attack or myocarditis |
| CK-BB | Stroke or brain injury; smooth muscle conditions |
Purpose
Diagnosis and monitoring of muscle injuries, muscular dystrophy, rhabdomyolysis and myositis. It can also be used to assess the severity of heart damage or stroke.
Results
High CK usually indicates muscle damage. Timing: after some injuries, CK levels may not reach their peak for up to two days, so repeat measurement may be needed.
Normal Values
Laboratory specific. The source notes that ranges depend on age, sex and race, as well as on muscle mass and level of physical activity.
Risks and Limitations
Common causes of falsely high results:
- Intense exercise
- Statin medications (may cause muscle damage)
- Alcohol consumption
Troponin is preferred for diagnosing a heart attack:
The troponin test is preferred for diagnosing a heart attack because it detects heart muscle damage more effectively.
In other words, CK-MB does not replace troponin.