Creatine Kinase (CPK), also known as Creatine Phosphokinase, is an enzyme found in various tissues, including the heart, brain, and skeletal muscles. The CPK test measures the level of this enzyme in the blood and is commonly used to diagnose muscle damage or injury. Elevated CPK levels can indicate conditions such as heart attacks (when the CK-MB fraction is elevated), muscle disorders, or trauma to muscles. There are different isoforms of CPK (such as CK-MM for skeletal muscle, CK-MB for heart muscle, and CK-BB for brain tissue), and the test can help determine the specific source of muscle damage.