Creatine Phospho Kinase MB

Creatine Phosphokinase-MB (CK-MB) is an enzyme found primarily in heart muscle cells. It is one of three isoenzymes of creatine kinase (CK), with the others being CK-MM (found in skeletal muscle) and CK-BB (found in the brain).

Clinical Significance of CK-MB:

1. Cardiac Marker for Myocardial Infarction (Heart Attack):

   • CK-MB is released into the bloodstream when heart muscle cells are damaged.

   • Levels begin to rise 3–6 hours after a heart attack, peak at 12–24 hours, and return to normal within 48–72 hours.

   • This makes CK-MB useful in diagnosing acute myocardial infarction (AMI) and assessing reinfarction.

2. Differentiation from Skeletal Muscle Damage:

   • CK-MB is more specific to cardiac muscle than total CK, but small amounts can be found in skeletal muscle, leading to some false positives.

   • Troponin levels are now the preferred biomarker for heart attacks due to higher specificity.

3. Other Conditions That Can Elevate CK-MB:

   • Myocarditis (inflammation of the heart)

   • Cardiac surgery or trauma

   • Pulmonary embolism

   • Chronic kidney disease (due to reduced clearance)

Reference Range:

• Normal CK-MB levels vary by lab, but generally:

  • Serum CK-MB: 0–5 ng/mL (or <6% of total CK)

  • CK-MB Relative Index: <2.5% (ratio of CK-MB to total CK)