Creatine kinase (CK)
Muscle enzyme in the blood that can rise after muscle strain or muscle damage
Also known as
Definition
Creatine kinase (CK, also creatine phosphokinase, CPK) is an enzyme involved in supplying energy in cells. Most of it is found in skeletal muscle, with smaller amounts in the heart muscle and the brain. Normal wear and tear on muscles always releases some CK into the blood; when muscle, heart or brain tissue is damaged, more leaks out. The test is mainly used to detect and monitor muscle injuries and muscle diseases.
| Parameter | Value |
|---|---|
| Unit | U/L or µg/L (depending on the method) |
| Reference Range | Depends on age, sex, ethnic background, muscle mass and physical activity. MedlinePlus gives 10–120 µg/L for total CK; labs that report CK as enzyme activity in U/L use their own ranges. The reference range in your own report is what counts; discuss it with your doctor. |
Agree on your personal target range with your doctor.
Values in µg/L (mass) and U/L (enzyme activity) cannot be converted directly into each other. Only compare results reported in the same unit.
↓ What a low value means
Which CK level is normal for you depends on factors such as age, sex, muscle mass and physical activity. A low value is therefore always considered together with these factors. If anything is unclear, ask your doctor.
↑ What a high value means
Elevated CK usually points to strain on or damage to muscle tissue, for example after intense exercise, accidents, burns or seizures. It may also be linked to muscle diseases such as muscular dystrophies or myositis, rhabdomyolysis, inflammation of the heart muscle, heart attack, stroke or thyroid disorders. Certain medicines such as statins, as well as alcohol, can also raise the value. After some injuries, CK only peaks up to two days later. The total value does not show where the CK comes from; isoenzyme testing is used for that. Discuss elevated results with your doctor.
When to test
Usually no special preparation is needed. To make the result meaningful, your doctor may ask you to avoid intense exercise and alcohol for a few days beforehand. The test is ordered, for example, for muscle pain, muscle weakness or dark urine, after muscle injuries, or while taking medicines that can damage muscles, such as statins.
Frequently asked questions
Why can CK be elevated after exercise? +
Intense exercise strains skeletal muscle, which releases more CK into the blood, mainly the CK-MM form. That is why you are often advised to avoid intense training for a few days before a blood draw. Whether an elevated value can be explained by exercise alone is for your doctor to judge.
What is the difference between CK-MM, CK-MB and CK-BB? +
They are three forms (isoenzymes) of CK. High CK-MM usually comes from skeletal muscle, high CK-MB usually from the heart muscle, and high CK-BB may be related to the brain or to smooth muscle, for example in the digestive tract. Isoenzymes are measured when the source of an elevated total value is unclear.
Is CK still used to diagnose a heart attack? +
In certain cases, yes. Today troponin is measured more often because it is better at showing damage to the heart muscle.
Why is CK sometimes measured more than once? +
After some injuries, CK only reaches its peak up to two days later. Repeated measurements show whether the value is rising or falling; levels that stay high or keep rising may indicate that muscle damage is ongoing.
Creatine kinase (CK)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.