Creatine Kinase-MB
CK-MB· also: CKMB, Creatine Kinase MB
Clinical Overview
CK-MB is an isoenzyme of creatine kinase found predominantly in cardiac muscle. It was the standard cardiac biomarker before troponin became widely available. CK-MB rises 4–6 hours after MI, peaks at 12–24 hours, and normalizes within 48–72 hours — faster than troponin. Its shorter window of positivity is used to diagnose re-infarction.
Why This Test Matters
CK-MB has largely been replaced by high-sensitivity troponin for MI diagnosis, which is more specific and sensitive. However, CK-MB retains clinical utility for timing myocardial injury (its faster return to normal allows detection of a second MI when troponin remains elevated from the first) and for assessing completeness of reperfusion after thrombolysis (an early CK-MB peak after thrombolysis suggests successful reperfusion).
Reference RangesWHO/IFCC standards
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 0 – 25 | U/L | — |
Also reported in: %.
What Causes Abnormal Results?
High CK-MB Causes
- Acute myocardial infarction
- Myocarditis
- Cardiac surgery or cardioversion
- Skeletal muscle trauma (when total CK is also very high)
- Rhabdomyolysis (a small amount of CK-MB is in skeletal muscle)
Low CK-MB Causes
- Not clinically significant (low or undetectable is normal)
Signs & Symptoms to Watch For
How to Prepare for This Test
No special preparation. Serial measurements are most useful — typically at 0, 6, and 12 hours in suspected MI.
Factors That Can Affect Results
- Skeletal muscle injury with high CK-MB fraction (macro-CK, athlete training)
- Hemolysis
- Myopathy (some skeletal muscle diseases express CK-MB)
Related Topics
Frequently Asked Questions
Is CK-MB still useful when troponin is available?
CK-MB is still used in specific situations: (1) detecting re-infarction in a patient with a recent MI where troponin remains elevated — a new CK-MB rise after normalization confirms a new event; (2) assessing reperfusion after thrombolysis — a rapid, early CK-MB peak (washout phenomenon) suggests successful clot dissolution; (3) estimating infarct size. For initial MI diagnosis, high-sensitivity troponin is always preferred.