Creatine Kinase-NAC

🔬 What is CK-NAC?

Creatine Kinase (CK) is an intracellular enzyme that catalyzes:

$$\text{Creatine phosphate + ADP}\leftrightarrow \text{Creatine + ATP}$$

CK-NAC refers to total CK activity measured using N-acetylcysteine (NAC) as an activator in the assay.

• NAC activates CK by maintaining sulfhydryl (–SH) groups in a reduced state.

• It measures total CK activity (not isoenzymes).

❤️ Clinical Significance

1️⃣ Marker of Muscle Damage

CK-NAC rises whenever there is muscle cell injury (skeletal or cardiac).

Common causes:

• 💪 Myopathies (e.g., muscular dystrophy)

• 🏋️ Strenuous exercise

• 🚗 Trauma / crush injury

• ⚡ Intramuscular injections

• 🔥 Burns

2️⃣ Myocardial Infarction (MI)

• CK rises 3–6 hours after MI

• Peaks at 18–24 hours

• Returns to normal in 2–3 days

⚠ However, total CK (CK-NAC) is not specific for cardiac muscle.
It has largely been replaced by:

• Cardiac troponins (preferred)

• CK-MB for better cardiac specificity

3️⃣ Rhabdomyolysis

Very high CK levels (often >5000 IU/L) suggest:

• Severe skeletal muscle breakdown

• Risk of acute kidney injury

4️⃣ Monitoring Muscle Disorders

Used in:

• Polymyositis

• Dermatomyositis

• Muscular dystrophies

• Drug-induced myopathy (e.g., statins)

5️⃣ Neurological Conditions

Mild elevation may be seen in:

• Seizures

• Stroke

• Hypothyroid myopathy

📊 Reference Range

• Adult males: ~ 38–174 IU/L

• Adult females: ~ 26–140 IU/L
  (Varies by laboratory)

⚠️ Limitations

• Poor cardiac specificity

• Elevated in many non-cardiac conditions

• Must be interpreted with clinical findings and other biomarkers