Creatine Kinase (CK)

Muscle damage marker — elevated after intense exercise or injury.

What it is

CK (also known as creatine kinase or CPK) is an enzyme found primarily in skeletal muscle, cardiac muscle, and the brain. When muscle cells are damaged, CK leaks into the blood.

Why it matters

Elevated CK can indicate muscle damage from intense exercise, treatment-related myopathy, or, in severe cases, rhabdomyolysis. Some drugs used in cancer care (particularly statins or immunotherapy) can cause muscle toxicity that CK will catch early.

How to test

Blood test. Avoid intense exercise 48 hours before testing for baseline readings.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

Men: 38–174 U/L. Women: 26–140 U/L. Context-dependent — elevated after hard exercise is normal.

How often

Every 6–12 months, or if experiencing muscle pain or weakness.