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What is the best way to test for rhabdomyolysis on labs?

Rhabdomyolysis is characterized by skeletal muscle damage resulting in a release of intracellular components including creatine kinase, AST, ALT, LDH, and aldolase, as well as myoglobin, potassium, and other electrolytes. Rhabdomyolysis can be life-threatening due to associated hyperkalemia, renal failure, and compartment syndrome.

Creatinine kinase (CK) (also known as creatinine phosphokinase/CPK) is considered the most sensitive lab marker for muscle injury.

Khan, F Y. “Rhabdomyolysis: a review of the literature.” The Netherlands journal of medicine vol. 67,9 (2009): 272-83

A cut-off for CK/CPK of 1000 U/L is commonly used in diagnosing rhabdomyolysis, and a level above 5000 U/L may reflect kidney damage. Elevated myoglobin may also reflect kidney damage depending on its peak 6-8 hours after injury.  

Cervellin, Gianfranco et al. “Non-traumatic rhabdomyolysis: Background, laboratory features, and acute clinical management.” Clinical biochemistry vol. 50,12 (2017): 656-662. doi:10.1016/j.clinbiochem.2017.02.016

In patients with a CK/CPK of 1000 U/L or greater, 93.1% had an elevated AST of greater than 40 U/L, and 75% had an ALT above 40 U/L. Concentrations of AST trended down as CK declined.  

Weibrecht, Kathryn et al. “Liver aminotransferases are elevated with rhabdomyolysis in the absence of significant liver injury.” Journal of medical toxicology : official journal of the American College of Medical Toxicology vol. 6,3 (2010): 294-300. 

Serum myoglobin, bound to circulating globulins, is usually maintained at a low level of 0-0.003 mg/dL. Levels above 0.5 mg/dL may start to overwhelm serum protein binding capacity, and myoglobin will be excreted in the urine.

Keltz, Eran et al. “Rhabdomyolysis. The role of diagnostic and prognostic factors.” Muscles, ligaments and tendons journal vol. 3,4 303-12. 24 Feb. 2014