What laboratory tests are recommended for a patient with rhabdomyolysis?

Laboratory Tests for Rhabdomyolysis

For patients with rhabdomyolysis, essential laboratory tests include serum creatine kinase (CK), urinalysis for myoglobinuria, comprehensive metabolic panel, complete blood count, and electrocardiogram to monitor for complications. 1

Core Laboratory Tests

Immediate Testing

• Serum Creatine Kinase (CK)

  • Diagnostic threshold: At least 10 times the upper limit of normal 1, 2
  • Monitor every 6-12 hours in acute phase 1
  • Can peak 24-72 hours after muscle injury 1
  • May reach levels as high as 100,000 IU/L or higher 2, 3

• Urinalysis

  • Check for myoglobinuria (tea/cola-colored urine) 1
  • Positive for blood on dipstick but negative for RBCs on microscopy 1
  • Note: The classic triad of myalgia, weakness, and pigmenturia occurs in less than 10% of cases 1, 2

• Plasma Myoglobin

  • Confirms muscle breakdown 1
  • Rises earlier than CK but has shorter half-life (2-3 hours) 1
  • May return to normal while CK remains elevated 1

Renal and Electrolyte Monitoring

• Comprehensive Metabolic Panel

  • Serum creatinine and BUN to assess renal function 1
  • Electrolytes with particular attention to:
    • Potassium (hyperkalemia is common and potentially life-threatening) 1
    • Calcium (hypocalcemia may occur) 1
    • Phosphorus (hyperphosphatemia may develop) 1
  • Acid-base status (metabolic acidosis may be present) 1

• Urine Output Monitoring

  • Target urine output >300 mL/hour during treatment 1

Additional Testing

• Complete Blood Count (CBC)

  • To assess for infection or inflammation 1

• Electrocardiogram (ECG)

  • To assess for cardiac complications and effects of electrolyte abnormalities 1

• Arterial Blood Gases

  • For patients with SaO₂ <92% or features of severe illness 1

• Chest Radiograph

  • Consider if respiratory symptoms are present 1

Testing for Recurrent Cases

For patients with recurrent rhabdomyolysis or suspected genetic cause:

• Genetic Testing

  • Consider specific gene panels for:
    • Glycogen storage diseases
    • Fatty acid oxidation disorders
    • Mitochondrial disorders
    • Muscular dystrophies
    • Ion channelopathies 1

• Autoimmune Panel

  • To differentiate from inflammatory myositis 1
  • Inflammatory markers are typically higher in myositis than rhabdomyolysis 1

Monitoring Protocol

• Monitor CK levels every 6-12 hours in acute phase 1
• Follow CK until trending down toward normal 1
• Monitor renal function and electrolytes at least daily until stable 1
• For patients on statins with elevated CK, check renal function and monitor CK every 2 weeks 1

Important Caveats

• Diagnostic Pitfall: Relying solely on the classic triad (myalgia, weakness, pigmenturia) will miss >90% of cases 2
• Treatment Timing: Early recognition and aggressive fluid resuscitation are critical to prevent acute kidney injury, which occurs in up to 57% of untreated cases 1, 4
• Compartment Syndrome: Monitor for signs of pain, tension, paresthesia, and paresis in affected limbs 1
• Nephrology Consultation: Recommended for all cases with acute kidney injury 1
• Medication Review: Avoid all nephrotoxic medications (NSAIDs, ACE inhibitors/ARBs, certain antibiotics) 1

Remember that while CK level correlates with muscle damage severity, it does not reliably predict renal outcomes, as even extremely high CK levels (>1,000 IU/L) can be associated with full renal recovery 3.