Creatine kinase isoenzymes

Creatine kinase (CK) is an enzyme found mainly in skeletal muscle, cardiac muscle, and the brain. When these tissues are damaged, CK is released into the bloodstream. The test measures CK isoenzymes—different versions of this enzyme that come from different tissues. CK-MB is specific to heart muscle, CK-BB to brain, and CK-MM to skeletal muscle. This breakdown helps clinicians identify which tissue is damaged. Elevated CK suggests muscle injury, heart attack, rhabdomyolysis, or neurological damage, depending on which isoenzyme is elevated.