According to the MedlinePlus, normal CPK levels are between 10 and 120 micrograms per liter. These normal values may differ among different laboratories throughout the United States.
CPK, or creatine phosphokinase, is an enzyme that is found in the skeletal muscle, brain and heart. It can be measured through a simple venipuncture states MedlinePlus. The test is ordered whenever an injury to the muscle, brain or heart is suspected. High levels of CPK in the blood indicate that an injury has occurred in one of these areas. High levels may also indicate that the patient is having a heart attack or has various muscle disorders.