What are the diagnostic tests for rhabdomyolysis (muscle breakdown disease)?

Diagnostic Tests for Rhabdomyolysis

The primary diagnostic test for rhabdomyolysis is serum creatine kinase (CK) measurement, with levels typically exceeding 1000 U/L or at least 5 times the upper limit of normal. 1

Core Laboratory Tests

• Serum creatine kinase (CK): The most sensitive laboratory marker for muscle injury and the definitive diagnostic test for rhabdomyolysis 1, 2
• Serum myoglobin: Released from damaged muscle tissue and can be detected earlier than CK, though it has a shorter half-life 3
• Complete electrolyte panel: Essential to assess for:
  • Hyperkalemia (can lead to cardiac arrhythmias) 4, 3
  • Hypocalcemia (early phase) 3
  • Hyperphosphatemia 3
  • Hyperuricemia 2
• Renal function tests: Creatinine and BUN to assess for acute kidney injury, which occurs in 15-33% of patients 5
• Urinalysis: To check for myoglobinuria, which may present as tea-colored or red-brown urine 6, 1

Additional Tests Based on Clinical Context

• Liver function tests: To assess for hepatic involvement and distinguish between hepatocellular and other patterns of injury 3
• Coagulation studies: To evaluate for disseminated intravascular coagulation, which can be a complication of severe rhabdomyolysis 3
• Arterial blood gas analysis: To assess for metabolic acidosis, which commonly occurs in severe rhabdomyolysis 3
• ECG and cardiac troponin: To rule out cardiac involvement, especially in severe cases 3

Etiology-Specific Testing

• Toxicology screen: When drug or toxin exposure is suspected 6, 5
• Viral studies: If viral myositis is suspected 3
• Autoimmune markers: Such as ANA, ASMA, and ANCA if autoimmune myositis is suspected 3
• Genetic testing: For recurrent cases or those with family history suggesting hereditary muscle enzyme defects 6, 5
• EMG and MRI: May be useful in cases of inflammatory myositis to differentiate from rhabdomyolysis 7

Important Clinical Considerations

• Urine myoglobin testing by dipstick/ultrafiltration has poor sensitivity (positive in only 19% of cases) and should not be relied upon to exclude rhabdomyolysis 5
• Initial creatinine values are better predictors of mortality and acute kidney injury than initial CK levels 8
• CK levels typically peak within 24-72 hours after muscle injury and decline by approximately 40% per day with adequate hydration 1
• Serial CK measurements are important to monitor the course of rhabdomyolysis 3
• Compartment syndrome assessment should be performed in traumatic cases, with early signs including pain, tension, paresthesia, and paresis 3

Special Populations

• For patients with recurrent rhabdomyolysis (approximately 11% of cases), consider evaluation for underlying myopathies or muscle metabolic defects 5
• In patients with idiopathic hyperCKaemia where full neurological evaluation has excluded other causes, investigation for malignant hyperthermia susceptibility may be warranted 7
• For patients with immune checkpoint inhibitor therapy, monitor for myositis with rash as a potential cause of rhabdomyolysis 4

Remember that early diagnosis and prompt treatment of rhabdomyolysis are essential to prevent complications such as acute kidney injury, which occurs in up to 46% of hospitalized patients with rhabdomyolysis 5.