Creatine Kinase-MB

🔬 What is CK-MB?

Creatine kinase (CK) has three isoenzymes:

• CK-MM – Skeletal muscle

• CK-BB – Brain

• CK-MB – Predominantly cardiac muscle

CK-MB is found mainly in myocardium (≈15–40% of total CK in heart), making it relatively specific for cardiac muscle injury.

❤️ 1️⃣ Diagnosis of Acute Myocardial Infarction (AMI)

CK-MB rises when myocardial cells are damaged.

⏱ Time Course After MI

• Rises: 3–6 hours

• Peaks: 12–24 hours

• Returns to normal: 48–72 hours

Because it normalizes quickly, CK-MB is useful in detecting reinfarction (second MI within a few days).

🔁 2️⃣ Detection of Reinfarction

If CK-MB rises again after having returned toward normal, it suggests:

• Recurrent myocardial injury

• Extension of infarct

This is an important advantage over troponins, which remain elevated for 7–14 days.

🏥 3️⃣ Assessment After Cardiac Procedures

CK-MB may rise after:

• Cardiac surgery

• Percutaneous coronary intervention (PCI)

• Defibrillation

It helps assess procedure-related myocardial damage.

📊 4️⃣ Differentiating Cardiac from Skeletal Muscle Injury

Total CK can rise due to:

• Trauma

• Myopathies

• Strenuous exercise

• > 2.5–3% → Suggests cardiac source

• < 2% → Usually skeletal muscle origin

⚠️ Other Causes of Elevated CK-MB

• Myocarditis

• Cardiac trauma

• Severe skeletal muscle injury

• Chronic renal failure

• Rhabdomyolysis

Thus, interpretation must always correlate with clinical findings and ECG.