CK levels refer to the amount of creatine kinase (CK) in the blood, which is a type of protein called an enzyme. CK is mostly found in skeletal muscles, but it can also be found in the heart and brain tissues. A small amount of CK in the blood is normal, but higher amounts can indicate muscle damage or disease. Elevated CK levels may indicate skeletal muscle, heart, or brain damage or degeneration, either chronic or acute. A CK test is most often used to diagnose and monitor muscular injuries and diseases, such as muscular dystrophy. The test can also help show if you have damage to your heart or other muscles. CK consists of three subunits, CK-MB, CK-MM, and CK-BB, and testing for these isoenzymes can be useful when the muscle damage source is unclear. CK levels can be slightly elevated in nerve disorders like Charcot-Marie-Tooth disease, amyotrophic lateral sclerosis, or spinal muscular atrophy, or grossly elevated in DMD or inflammatory myopathies. CK levels can vary depending on gender, race, age, muscle mass, and physical activity. The normal range of CK levels can slightly vary from laboratory to laboratory, but in general, a healthy range in females is 30 to 145 U/L, and for males, it’s 55 to 170 U/L.