Is Creatine Kinase (CK) Included in a Comprehensive Metabolic Panel (CMP)?
No, Creatine Kinase (CK) is not included in a standard Comprehensive Metabolic Panel (CMP). CK is a separate test that must be ordered independently when muscle or cardiac damage is suspected.
Components of a Standard CMP
A standard Comprehensive Metabolic Panel typically includes:
- Electrolytes: Sodium, potassium, chloride, bicarbonate
- Kidney function tests: BUN (blood urea nitrogen), creatinine
- Liver function tests: ALT, AST, alkaline phosphatase, bilirubin
- Protein levels: Total protein, albumin
- Glucose
- Calcium
Creatine Kinase Testing
Creatine Kinase is ordered separately from a CMP when there is clinical suspicion for:
- Myocardial injury: Though cardiac troponins have largely replaced CK-MB as the preferred marker for myocardial infarction diagnosis 1
- Skeletal muscle damage: Such as in rhabdomyolysis, trauma, or muscular disorders
- Certain neuromuscular diseases: Like Pompe disease where CK elevation is a sensitive marker 1
Clinical Significance of CK
When CK testing is indicated, it's important to understand:
CK has multiple isoenzymes:
- CK-MB: Primarily found in cardiac muscle
- CK-MM: Predominantly in skeletal muscle
- CK-BB: Found in brain tissue
For cardiac evaluation, guidelines from the American College of Cardiology/American Heart Association indicate that cardiac troponin is the preferred marker for diagnosing myocardial infarction, with CK-MB considered an acceptable alternative only when troponin testing is unavailable 1.
CK levels can be significantly elevated (>2,000 U/L) in various conditions without indicating a need for intervention, particularly after strenuous exercise 2.
When to Order CK
CK should be ordered separately when:
- Evaluating suspected myocardial injury (though troponins are preferred)
- Assessing for rhabdomyolysis or muscle damage
- Monitoring certain muscular diseases
- Evaluating patients on medications with potential muscle toxicity (e.g., statins)
- Screening for immune checkpoint inhibitor toxicity (where total CK is recommended as part of pre-treatment screening) 1
Common Pitfalls
Assuming CK is part of routine testing: Since CK is not included in a CMP, clinicians must specifically order it when indicated.
Relying on CK-MB alone for cardiac evaluation: Current guidelines strongly favor troponin over CK-MB for diagnosing myocardial infarction due to superior sensitivity and specificity 1.
Misinterpreting elevated CK: CK can be significantly elevated after exercise or in various non-cardiac conditions, requiring clinical correlation 2.
In summary, CK testing remains clinically valuable in specific scenarios but must be ordered separately from the standard CMP when indicated.