What is CKMB (Creatine Kinase-MB)?
CKMB (Creatine Kinase-MB) is a cytosolic carrier protein for high-energy phosphates that has long been the standard marker for the diagnosis of myocardial infarction, though it is less sensitive and less specific than cardiac troponins for detecting myocardial injury. 1
Characteristics of CKMB
- CKMB is an isoenzyme of creatine kinase that is primarily found in cardiac muscle tissue
- It is released into the bloodstream when cardiac muscle cells are damaged
- Low levels of CKMB can be found in the blood of healthy persons 1
- Elevated levels can occur with damage to skeletal muscle, limiting its specificity 1
Comparison with Cardiac Troponins
| Characteristic | Troponin | CKMB |
|---|---|---|
| Cardiac specificity | Higher | Lower |
| Sensitivity for small MI | Higher | Lower |
| Duration of elevation | 4-14 days | 24-36 hours |
| Risk stratification value | Superior | Good but less powerful |
| Ability to detect reinfarction | Limited | Better |
| [2] |
Clinical Utility of CKMB
Despite being largely replaced by troponins, CKMB remains useful in specific clinical situations:
Diagnosis of reinfarction (recurrent MI): Due to its shorter half-life compared to troponin, CKMB can help detect new cardiac damage in patients who recently had an MI 1
- A 20% increase in CKMB value in a second sample (taken 3-6 hours after the first) is diagnostic of reinfarction 1
Diagnosis of periprocedural MI: The diagnostic and prognostic value of CK-MB has been extensively validated in this context 1
Timing of MI: CKMB typically rises 4-6 hours after myocardial injury, peaks at 24 hours, and returns to normal within 36-48 hours 2
Measurement and Interpretation
- CKMB should be measured by mass immunoassays rather than older methods 1
- An increased CKMB value is defined as a measurement above the 99th percentile of the upper reference limit (URL) 1
- Gender-specific values should be employed 1
- The ratio of CKMB mass to total CK activity can help differentiate between cardiac and skeletal muscle injury
- A ratio >80 ng/U is suggestive of myocardial necrosis rather than skeletal muscle injury 3
Current Recommendations
While cardiac troponins have largely replaced CKMB as the preferred biomarker for detecting myocardial injury, CKMB can still provide complementary information in specific scenarios. The American College of Cardiology and American Heart Association acknowledge that CKMB can be useful when troponin results are not available or when evaluating for reinfarction in patients with persistently elevated troponin levels 1.
Limitations
- Less sensitive than troponin for detecting small amounts of myocardial damage
- Less specific for cardiac injury (can be elevated in skeletal muscle damage)
- The use of older biochemistry assays like alanine transaminase, aspartate transaminase, and lactate dehydrogenase should generally be avoided in contemporary practice 1