CK
What it measures, and what changes the number.
CK, or creatine kinase, is an enzyme found mainly in skeletal muscle, with smaller amounts in heart muscle and the brain. The test measures its activity in the blood, where it appears when muscle cells release their contents.
It is often read with CK-MB, which looks at the heart-related form, and with AST, ALT and aldolase, since some of these enzymes are also present in muscle and help show whether a change is coming from muscle or liver.
Recent physical activity has a large effect on this number. Strenuous exercise, muscle injury, falls and injections into a muscle can raise CK for several days, so recent activity is relevant when comparing results. Muscle mass also influences it, and haemolysis in the sample can interfere with some methods. Labs may print it as Creatina Quinasa (CK).