To Measure Activity of Creatine Kinase in Serum
Creatine kinase (CK), also called creatine phosphokinase, exists as three isoenzymes, i.e., CK1, CK2, and CK3. Each isoenzyme is dimeric enzyme composed of subunits M (muscle) or B (brain). The isoenzyme CK1 contains subunit BB and occurs primarily in the brain. CK2 possess subunit MB and are found in the heart. Skeletal muscles primarily contain the MM isoform (CK3). Healthy individuals typically contain the MM isoform and a small amount of the MB isoform in their serum. The enzyme is not found in the liver, kidney, and blood cells. Various conditions including skeletal muscle injury and myocardial damage release CK-MB into the bloodstream. In myocardial infarction, levels of both CK-total and CK-MB increase significantly, but CK-MB is considered a specific cardiac marker.