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CK-MB Index Calculator
The CK-MB Relative Index helps distinguish between elevations in Creatine Kinase (CK) caused by skeletal muscle damage versus those caused by myocardial infarction (heart attack).
While Troponin is the gold standard for diagnosing acute coronary syndromes, the CK-MB Index remains useful, particularly for detecting re-infarction shortly after an initial event, as CK-MB levels normalize faster than Troponin.
Lab Values
InputsU/L (International Units)
ng/mL (Mass)
Results
Cutoff for MI: > 2.5 – 5%
Clinical Context
Formula:
Index (%) = (CK-MB [ng/mL] / Total CK [U/L]) × 100
Interpretation:
• < 2.5%: Suggests skeletal muscle injury (e.g., rhabdomyolysis, trauma, strenuous exercise).
• > 2.5 – 5%: Indeterminate / Grey Zone.
• > 5%: Highly suggestive of myocardial source (Acute MI).
Important Limitation: If Total CK is extremely high (e.g., > 10,000 U/L from severe trauma), the index may be artificially low even if there is concurrent cardiac injury. Always correlate with ECG and clinical symptoms.
Clinical References
How to Use This Calculator
Follow these steps to calculate the index.
Input Total CK
Enter the Total Creatine Kinase level from the chemistry panel.
Input CK-MB
Enter the CK-MB Mass level. Ensure the units match (ng/mL).
Interpret Result
A higher percentage indicates that a larger portion of the CK is coming from the heart muscle.
Frequently Asked Questions
Troponin is more specific and sensitive. However, Troponin stays elevated for 7-10 days. If a patient has chest pain 4 days after an MI, Troponin will still be high from the first event. CK-MB normalizes in 24-48 hours, so a new spike indicates a new injury (Re-infarction).
Rhabdomyolysis, intense gym workouts, intramuscular injections, falls, or statin use can elevate Total CK (skeletal source) without significantly raising CK-MB.