Rhabdomyolysis Diagnosis and Management

Initial Diagnostic Laboratory Tests

The American College of Physicians recommends immediate measurement of creatine kinase (CK), comprehensive metabolic panel with electrolytes, urinalysis for myoglobinuria, and serial monitoring of renal function, with CK ≥5-10 times the upper limit of normal being diagnostic for rhabdomyolysis 1
Comprehensive metabolic panel, including creatinine, BUN, electrolytes, glucose, calcium, and phosphorus, is essential for diagnosing rhabdomyolysis 1
Urinalysis should be performed to look for myoglobinuria, indicated by brown or dark urine that is positive for blood without red blood cells present 1
Complete blood count with differential should be done to evaluate for infection or other systemic processes 1

Potassium levels must be checked immediately and monitored closely, as hyperkalemia can precipitate life-threatening cardiac arrhythmias and cardiac arrest 1, 2
Calcium, phosphorus, and magnesium levels should be assessed for hypocalcemia and hyperphosphatemia, which are common complications of rhabdomyolysis 1
Arterial blood gas should be performed to assess for metabolic acidosis, which commonly occurs in severe rhabdomyolysis 1

Autoimmune markers, such as ANA, anti-CCP, rheumatoid factor, and myositis-specific antibodies, should be checked if autoimmune myositis is suspected 3, 1
Inflammatory markers, including ESR and CRP, should be assessed to evaluate for inflammatory processes 3
Viral studies should be considered if clinically indicated 1

ECG should be performed immediately to assess for arrhythmias related to hyperkalemia 1
Cardiac troponin should be checked in patients with severe rhabdomyolysis to rule out cardiac involvement 1

CK levels should be trended daily until declining, and IV fluids should be continued typically until CK <1,000 U/L 1
Electrolytes, particularly potassium, should be checked every 6-12 hours in severe cases 1
Renal function should be monitored daily until stable, with assessment of creatinine and BUN 1
Urine output should be monitored hourly, with a target of ≥300 mL/hour 2

Mild rhabdomyolysis is characterized by CK elevation but <15,000 IU/L, normal renal function, and no significant electrolyte abnormalities 1, 2
Moderate rhabdomyolysis is characterized by CK 15,000-50,000 IU/L, mild renal dysfunction, and requires 3-6L fluid resuscitation per day 1, 2
Severe rhabdomyolysis is characterized by CK >50,000 IU/L, acute kidney injury, and requires >6L fluid resuscitation per day, with a high risk for complications 1, 2

The American College of Rheumatology recommends measuring additional muscle enzymes, including LDH, AST, ALT, and aldolase, as they are commonly elevated in rhabdomyolysis patients 4
Inflammatory markers, including ESR and CRP, should be evaluated to assess for inflammatory processes, as recommended by the Annals of the Rheumatic Diseases 4
Thyroid function tests should be performed to evaluate for hypothyroidism, which predisposes to statin-induced rhabdomyolysis, according to the Annals of the Rheumatic Diseases 4

Autoimmune markers, such as ANA, ASMA, ANCA, anti-CCP, rheumatoid factor, and myositis-specific antibodies, should be considered if autoimmune myositis is suspected, with guidance from the Annals of the Rheumatic Diseases 4
Viral studies should be performed if viral myositis is clinically suspected, and genetic and metabolic testing should be considered for recurrent rhabdomyolysis, including RYR1 and CACNA1S gene sequencing for malignant hyperthermia susceptibility, as recommended by the Annals of the Rheumatic Diseases 4