Creatine kinase (CK) is an intracellular enzyme present in skeletal muscle, myocardium & brain; smaller amounts in visceral tissues. Released after disruption of cell membranes due to hypoxia or other injury. Sustained increases in these levels can be a sensitive indicator of underlying muscle damage. CK may increase to as much as 30 times the upper limit within 24 hrs of strenuous physical activity, then slowly decline over next 7 days. The definitive diagnosis of rhabdomyolysis is reliably made by serologic testing for creatine kinase (CK). Elevated levels of CK are the hallmark of rhabdomyolysis. CK functions as an energy reservoir for ATP: Creatine + ATP = creatine kinase + ADP (adenosine diphosphate). CK has a half-life of 1.5 days; its level elevated in the first 12 hours, peaks during the first 3 days, and normalizes at around 5 days after injury. CK level five times the upper limit of normal (≈1000 U/L), without apparent cardiac or brain injury, confirms the diagnosis. Risk of developing AKI is usually low when the CK level is below 10,000 U/L. AKI at lower levels of CK noted with coexisting conditions, such as sepsis, hypotension, or underlying CKD. Myoglobin levels rise rapidly (within 3 hours) and peak prior to serum CK levels. Myoglobin has a short half-life of 2 - 3 hours and is rapidly excreted by the kidneys. Rapid and unpredictable metabolism makes serum myoglobin a less useful marker of muscle injury than CK, and is rarely used in assessing the risk of AKI. Satyendra Dhar, MD, @DharSaty #rhabdomyolysis #creatinekinase #CK #myoglobin
