Creatine kinase (CK or CPK) is an enzyme (protein) found in the muscles, including the heart.
High CK levels that return to normal within a few days indicate recent muscle damage. Normal CK levels therefore indicate no muscular problems or that these problems occurred several days before the test. CK levels that stay high for several weeks indicate a more chronic muscular disorder (muscular dystrophy or other genetic muscular diseases, other chronic conditions such as kidney failure, celiac disease, connective tissue diseases such as lupus or rheumatoid arthritis, thyroid or untreated adrenal disorders, and so on).
Extremely high CK levels can be caused by sustained muscular exercises (running, body building, physical fitness training) or by traumatic injuries to the muscles (heart attack, crushing, compression, epilepsy seizures, burns, electrocution, intramuscular injections, chills due to fever, and thromboses (phlebitis), which reduce blood flow in the muscles). Viral, bacterial, fungal or parasitic infections can also cause high CK levels, as can many drugs and toxins.
In very rare cases where the cause of a chronically high CK level cannot be found, the CK isoenzyme level may be measured.