Creatine kinase (CK), also called creatine phosphokinase, is an enzyme found mainly in skeletal muscle, heart muscle, and the brain. It plays an essential role in energy production by helping to convert creatine and ATP into phosphocreatine, which the body uses as a quick energy source during muscle contraction. Under normal conditions, only small amounts of CK circulate in the blood, but levels can rise when muscle tissue is stressed or damaged.
High CK levels are often seen after intense physical activity, particularly strength training or unaccustomed exercise. They can also result from muscle injury, inflammation, or conditions like rhabdomyolysis, where muscle fibres break down and release contents into the bloodstream. In some cases, medications such as statins, certain infections, or endocrine issues like hypothyroidism can also raise CK. For athletes or active individuals, temporarily raised CK is generally expected and returns to normal with adequate rest and recovery.
Low CK levels are less common and usually not concerning. They may be seen in people with low muscle mass, those who are inactive, or in rare cases, with muscle-wasting conditions or long-term steroid use. Occasionally, a low CK level might reflect poor nutritional status or underlying metabolic issues, but on its own, it’s not typically used as a diagnostic marker. CK is most useful when interpreted alongside other tests that reflect muscle function and systemic health#