What are the immediate tests and management for a patient suspected of having rhabdomyolysis?

Immediate Tests and Management for Suspected Rhabdomyolysis

For patients with suspected rhabdomyolysis, immediately obtain serum creatine kinase (CK), creatinine, and perform urinalysis for myoglobinuria, then initiate aggressive fluid resuscitation with isotonic saline targeting urine output >300 mL/hour to prevent acute kidney injury. 1

Diagnostic Tests

• Serum markers:

  • Creatine kinase (CK) - diagnostic threshold is ≥10 times upper limit of normal 1, 2
  • Monitor CK every 6-12 hours in acute phase 1
  • Complete metabolic panel including:
    • Electrolytes (particularly potassium, calcium, phosphorus)
    • BUN and creatinine
    • Liver function tests 1
  • Plasma myoglobin (rises earlier than CK but has shorter half-life of 2-3 hours) 1

• Urinalysis:

  • Check for myoglobinuria (tea/cola-colored urine)
  • Dipstick positive for blood but negative for RBCs on microscopy 1
  • Note: Urine myoglobin may be negative in up to 81% of cases despite rhabdomyolysis 3

• Additional tests:

  • Electrocardiogram to assess for cardiac complications and effects of electrolyte abnormalities 1
  • Consider chest radiograph if respiratory symptoms are present 1
  • Arterial blood gases for patients with SaO₂ <92% or features of severe illness 1

Immediate Management

1. Fluid Resuscitation:

   • Initiate aggressive hydration with isotonic saline (0.9% NaCl) 1
   • Target urine output >300 mL/hour 1, 4
   • Avoid potassium-containing fluids such as Lactated Ringer's 1

2. Electrolyte Management:

   • Monitor and urgently correct hyperkalemia if present 1
   • Address hypocalcemia only if symptomatic 1
   • Monitor and correct other electrolyte abnormalities as needed 4

3. Renal Protection:

   • Consider bicarbonate infusion for patients with acidosis 1, 4
   • Consider mannitol if urine output goals are not met despite adequate fluid resuscitation 4
   • Discontinue all nephrotoxic medications (NSAIDs, ACE inhibitors/ARBs, certain antibiotics) 1

4. Compartment Syndrome Assessment:

   • Monitor for signs of compartment syndrome: pain, tension, paresthesia, and paresis in affected limbs 1
   • Remove tight dressings and avoid limb elevation if compartment syndrome is suspected 1
   • Obtain urgent surgical consultation for fasciotomy if compartment syndrome is confirmed 1

5. Nephrology Consultation:

   • Consult nephrology for all cases with acute kidney injury 1
   • Consider renal replacement therapy for:
     • Severe hyperkalemia
     • Acidosis
     • Volume overload
     • Uremic symptoms 1

Monitoring

• Continue CK monitoring every 6-12 hours until trending down 1
• Monitor urine output hourly 1, 4
• Monitor electrolytes frequently, especially potassium and calcium 1
• Calculate McMahon score on admission (score ≥6 predicts need for renal replacement therapy) 5
• Continue IV fluids until CK levels are below 1,000 U/L 4

Important Clinical Considerations

• The classic triad of myalgia, muscle weakness, and pigmenturia is present in less than 10% of cases 1, 2
• Multiple etiologic factors often contribute to rhabdomyolysis and can lead to exceptionally high CK levels and worse outcomes 6
• Mortality rate is approximately 10% and significantly higher in patients who develop acute renal failure 2
• Recurrent rhabdomyolysis (occurring in about 11% of cases) may indicate an underlying genetic disorder that requires further investigation 1, 3

Common Pitfalls to Avoid

1. Relying solely on the classic triad for diagnosis (present in <10% of cases)
2. Delaying fluid resuscitation while waiting for laboratory confirmation
3. Using potassium-containing fluids for resuscitation
4. Failing to recognize and treat compartment syndrome promptly
5. Missing myoglobinuria due to its short half-life (urine myoglobin may be negative in up to 81% of cases) 3
6. Discontinuing fluid therapy too early before adequate CK clearance