From the Guidelines
Rhabdomyolysis is typically diagnosed when creatine kinase (CK) levels exceed 5 times the upper limit of normal, which is generally above 1,000 U/L, as indicated by the most recent and highest quality study 1.
Diagnosis and Thresholds
The diagnosis of rhabdomyolysis requires not only elevated CK levels but also supporting clinical features such as muscle pain, weakness, dark urine, and in some cases, evidence of kidney dysfunction.
- CK levels should be interpreted in clinical context, as some individuals may have elevated baseline CK levels due to factors like race, muscle mass, or physical activity.
- Many clinicians use a threshold of 10 times the upper limit of normal (approximately 2,000-3,000 U/L) or even higher values of 5,000-10,000 U/L to definitively diagnose rhabdomyolysis.
- The severity of rhabdomyolysis often correlates with CK levels, with values above 5,000 U/L indicating significant muscle breakdown and increased risk of complications such as acute kidney injury, as supported by 1.
Clinical Considerations
- Treatment typically involves aggressive intravenous fluid administration to prevent kidney damage, regardless of the exact CK level.
- The measurement of plasma myoglobin, which has an earlier peak plasma concentration than CPKs, may be more sensitive and specific than CPKs in identifying the risk of acute kidney injury, which is correlated with increased mortality 1.
- Assessment of kidney function by means of plasma creatinine test and plasma potassium test for hyperkalaemia can complement the diagnosis and management of rhabdomyolysis.
From the Research
Definition of Rhabdomyolysis and CK Levels
- Rhabdomyolysis is a serious and potentially life-threatening condition characterized by the breakdown of skeletal muscle and leakage of intracellular myocyte contents into the interstitial space and plasma, resulting in acute kidney injury (AKI) 2, 3, 4, 5, 6.
- The diagnosis of rhabdomyolysis is confirmed when the serum creatine kinase (CK) level is > 1000 U/L or at least 5x the upper limit of normal 4.
- A CK level at least 10 times the upper limit of normal is typically considered diagnostic of rhabdomyolysis 2, 5.
CK Levels and Rhabdomyolysis Severity
- Elevated CK levels are associated with increased renal damage and complications, with higher levels indicating greater severity 2, 6.
- CK levels can range from 10,000 to 200,000 or even higher in rhabdomyolysis, with exceptionally high levels (nearly 1 million) reported in some cases 6.
- A CK level of >16,000 IU/l may be associated with a higher risk of acute renal failure 2.
Importance of Early Recognition and Treatment
- Prompt recognition and management of rhabdomyolysis are crucial to preserving renal function and preventing life-threatening complications 2, 4, 5.
- Early and aggressive fluid replacement using crystalloid solution is the cornerstone of treatment for preventing and treating AKI due to rhabdomyolysis 4, 5.