The normal reference values for creatine kinase are 24-170 U/L for men and 24-150 U/L for women. When lower than 24 U/L, creatine kinase is low. Low creatine kinase is mainly caused by hyperthyroidism. In general, a low creatine kinase level is not very meaningful and should be combined with other cardiac enzymes, such as troponin, for a comprehensive diagnosis. First of all, it is important to know about creatine kinase, also called CK, which is mainly found in the cytoplasm and granulosa, and is an important kinase directly related to intracellular energy operation, muscle contraction, and ATP regeneration. It is abundant in skeletal muscle, cardiac muscle and smooth muscle, followed by lesser amounts in brain tissue, gastrointestinal tract, lung and kidney. Creatine kinase is most abundant in cardiac and skeletal muscle, and therefore creatine kinase activity can be used for the diagnosis of skeletal muscle disease as well as cardiac muscle disease. Creatine kinase is an important indicator in the myocardial enzyme profile and is clinically important in patients with acute myocardial infarction at the onset. An elevated creatine kinase indicates possible myocardial injury, but a low creatine kinase does not seem to be diagnostic. There is little clinical interest in reduced creatine kinase, and its clinical significance is not great, especially in relation to cardiac system disease.