What it measures
Creatine kinase is an enzyme found mainly in muscle, with smaller amounts in the heart and brain. When muscle is strained or damaged it leaks into the blood, so the level reflects recent muscle stress or damage.
Why people test it
- Checked when someone on a statin has muscle aches or weakness.
- Measured when looking into unexplained muscle pain, weakness or cramps.
- Used to check for muscle breakdown after an injury, a fall or certain medicines.
- Raised for several days after heavy lifting, long runs or a new type of training.
- Some athletes track it across training blocks as a sign of muscle load.
Typical range
Ranges vary by lab, method, age and sex, and your report shows the lab's own range. One NHS trust gives 40 to 320 U/L for men and 25 to 200 U/L for women. Source: Worcestershire Acute Hospitals NHS Trust: Creatine Kinase (Total).
Finger-prick or vein?
A vein draw is the usual route, and most providers offer it only that way. Finger-prick samples haemolyse more easily, which can upset the CK reading.
Hard exercise raises CK for several days, so a result taken soon after a heavy session can read high.