Clinical Significance of Creatine Kinase

Basic Characteristics and Function

Creatine kinase (CK) is an enzyme that catalyzes the reversible reaction of phosphocreatine, magnesium adenosine diphosphate (MgADP-), and a hydrogen ion to MgATP2- and creatine, playing a crucial role in cellular energy metabolism by either re-phosphorylating ADP to ATP or storing immediately available energy in the form of phosphocreatine, according to the American College of Sports Medicine 1, 2
CK has a molecular size of approximately 82 kDa, which prevents it from entering the bloodstream via the transepithelial pathway under normal conditions, as reported in Sports Medicine 1

CK-MB has historically been the standard marker for myocardial infarction diagnosis before troponins became available, and remains useful in specific clinical scenarios, such as diagnosis of early reinfarction due to its shorter half-life, according to the American Heart Association 3, 4
CK-MB is useful in evaluating periprocedural myocardial injury during cardiac interventions, as stated by the American College of Cardiology 3, 4
Elevated total CK without elevated CK-MB suggests skeletal muscle injury rather than cardiac injury, as recommended by the American College of Sports Medicine 3

CK levels commonly increase after unaccustomed exercises, especially those involving eccentric contractions, according to the American College of Sports Medicine 1
The release mechanism of CK into bloodstream following exercise is complex and not fully understood, as reported in Sports Medicine 1

When measuring CK-MB, mass immunoassays are preferred over older methods, as recommended by the American Heart Association 3, 4
In pediatric patients with motor delays and low muscle tone, CK measurement is valuable for screening conditions like Duchenne muscular dystrophy, where levels typically exceed high levels of enzyme activity, as stated by the American Academy of Pediatrics 5