Creatine KinaseU/L
Muscle damage
Also known as: CK
Typical optimal range
39–308 U/L
A typical reference range is around 39–308 U/L, though exact cut-offs vary between laboratories, so your result should always be interpreted alongside your own lab's reference interval. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of CK in the context of statin use follows NICE guideline NG238 on cardiovascular disease risk reduction, and NHS laboratory guidance supports contextualising results alongside symptoms and recent physical activity.
What is Creatine Kinase?
Creatine kinase (CK) is an enzyme found mainly in skeletal muscle, heart muscle, and the brain. When muscle cells are damaged or stressed, CK leaks into the bloodstream, making it a useful marker of muscle injury. Measuring CK can help clinicians assess the degree of muscle damage, whether from exercise, medication side effects, or less commonly, a more serious underlying condition.
What a high Creatine Kinase means
A raised CK level signals that muscle cells have been under stress and are leaking their contents into the bloodstream — it's a prompt to look at the context rather than a diagnosis in itself.
- Intense or eccentric exercise. Heavy resistance training, long-distance running, or any unaccustomed exercise — especially movements that involve lengthening muscles under load — can raise CK five to ten times above the upper reference limit. This is a normal physiological response and typically resolves within a few days of rest.
- Statin therapy. Statins, which are widely prescribed in the UK for cholesterol management, can cause muscle-related side effects in some people. A raised CK alongside muscle pain or weakness in someone taking a statin is worth discussing with a GP, as NICE guidance advises checking CK in this setting.
- Rhabdomyolysis. In rare cases, severe muscle breakdown — called rhabdomyolysis — causes very markedly elevated CK (often many times the upper limit of normal) and can affect kidney function. This is uncommon and usually associated with extreme exertion, crush injury, certain medications, or serious illness, rather than routine exercise.
The timing of the blood test relative to exercise matters enormously — CK can remain elevated for 48–72 hours or more after a hard session, so a single elevated result in an active person is rarely cause for alarm without other symptoms.
What a low Creatine Kinase means
A low CK level is not generally considered clinically significant and is usually nothing to be concerned about.
Low CK has no well-established clinical meaning in otherwise healthy individuals and does not typically require further investigation.
Should I be worried?
A single raised CK result, particularly if you have exercised recently, is very common and often entirely benign. Before drawing conclusions, it is worth considering whether you trained hard in the 48–72 hours before the test, as this alone can push CK well above the reference range. If your CK is persistently elevated on repeat testing, or if it is raised alongside muscle pain, weakness, or dark urine — or if you are taking a statin — it is sensible to speak with your GP. They may want to repeat the test after a period of rest, check kidney function, thyroid function (an underactive thyroid can raise CK), and review any medications you are taking. Very high levels with symptoms warrant prompt assessment.
What actually helps
Keeping CK within a healthy range is largely about allowing adequate muscle recovery and supporting general muscle health through lifestyle habits.
- Rest before testing. Avoiding intense exercise for at least 48–72 hours before a planned CK blood test gives muscle cells time to recover and ensures your result reflects your baseline rather than post-exercise leak.
- Gradual training progression. Introducing new or intense exercise gradually — particularly eccentric movements like downhill running or heavy resistance training — reduces the degree of muscle damage and the resulting CK spike over time as muscles adapt.
- Adequate hydration. Staying well hydrated supports healthy kidney function and blood flow to muscles, which aids recovery. Dehydration can compound muscle stress and is a recognised contributing factor in exercise-related muscle breakdown.
- Sleep and recovery. Muscle repair happens predominantly during rest and sleep. Consistently getting seven to nine hours of sleep supports the body's natural recovery processes and helps keep CK levels from remaining chronically elevated.
There is good supporting evidence that certain dietary patterns and foods can help maintain muscle integrity and reduce oxidative stress on muscle tissue.
Tart cherry juice
Several well-conducted trials have shown that tart cherry juice can reduce CK elevation and muscle soreness following intense exercise, likely due to its high anthocyanin content with antioxidant and anti-inflammatory properties.
Oily fish (e.g. salmon, mackerel, sardines)
Rich in omega-3 fatty acids, oily fish have evidence supporting reduced exercise-induced muscle damage and inflammation; the NHS recommends at least one portion of oily fish per week.
Protein-rich foods (e.g. eggs, legumes, lean meat)
Adequate dietary protein is essential for muscle repair following exercise-induced damage; spreading intake across meals supports muscle protein synthesis throughout the day.
Colourful fruits and vegetables
A diet rich in antioxidants from varied fruit and vegetables helps mitigate the oxidative stress that contributes to muscle cell damage and CK release.
Whole grains and complex carbohydrates
Replenishing muscle glycogen after exercise through carbohydrate intake supports recovery and reduces the extent to which muscles are broken down for energy during subsequent sessions.
Track your own Creatine Kinase
Upload a lab PDF and Better Days trends Creatine Kinase over time, flags it when it drifts, and suggests foods that help.
More in Inflammation
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.