Laboratory Tests for Suspected Rhabdomyolysis
The essential laboratory tests for a patient with suspected rhabdomyolysis should include serum creatine kinase (CK), complete electrolyte panel (especially potassium, calcium, and phosphorus), renal function tests, urinalysis, and plasma myoglobin. 1, 2
Core Laboratory Tests
- Serum creatine kinase (CK) - The diagnosis is confirmed when levels exceed 1000 U/L or at least 5 times the upper limit of normal 2
- Serum myoglobin - Important for diagnosis, especially in cases where CK may not be elevated 1, 3
- Complete electrolyte panel - Must include potassium, calcium, phosphorus, and magnesium 1
- Renal function tests - Blood urea nitrogen (BUN) and serum creatinine to assess kidney function 1, 2
- Urinalysis - To check for myoglobinuria (appears as "blood" on dipstick with few or no RBCs on microscopy) 2, 3
Additional Essential Tests
- Liver function tests - To assess hepatic involvement and distinguish between patterns of injury 1
- Coagulation studies - To evaluate for disseminated intravascular coagulation, a potential complication 1
- Arterial blood gas - To assess for metabolic acidosis in severe cases 1
- ECG and cardiac troponin - To rule out cardiac involvement, especially in severe cases 1
Monitoring Parameters
- Serial CK measurements - To track disease progression and response to treatment 2
- Serial electrolyte measurements - Particularly potassium, as hyperkalemia can lead to life-threatening cardiac arrhythmias 4, 1
- Urine output - Should be monitored closely to assess kidney function and response to fluid therapy 4
- Compartment pressures - When compartment syndrome is suspected (pain, tension, paresthesia, paresis) 5, 1
Etiology-Specific Testing
- Viral studies - If viral myositis is suspected 1
- Autoimmune markers - If autoimmune myositis is suspected (ANA, ASMA, ANCA) 1
- Toxicology screen - If drug or toxin exposure is suspected 1
Clinical Pitfalls to Avoid
- Relying solely on CK levels - Some cases of rhabdomyolysis-induced acute kidney injury can occur with normal CK levels 3
- Delaying treatment while awaiting laboratory confirmation - Early fluid resuscitation is critical and should not be delayed 4, 6
- Failing to monitor for compartment syndrome - Early signs include pain, tension, paresthesia, and paresis; late signs (pulselessness and pallor) often indicate irreversible damage 5, 1
- Overlooking electrolyte abnormalities - Particularly hyperkalemia, which requires urgent treatment to prevent cardiac arrhythmias 4, 1
Risk Assessment
- Calculate McMahon score on admission - A score ≥6 predicts need for renal replacement therapy 2
- Monitor for signs of acute kidney injury - Rising creatinine, decreased urine output 2, 7
- Assess for risk factors that may complicate management - Pre-existing renal disease, dehydration, acidosis 4, 7
Remember that early diagnosis and aggressive fluid resuscitation are the cornerstones of preventing complications from rhabdomyolysis, particularly acute kidney injury 2, 6, 8.