whick ck to test for rhabdomyolysis
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rhabdomyolysis diagnosis creatine kinase
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Here is a complete answer based on authoritative emergency medicine textbooks:
Testing for Rhabdomyolysis
Primary Test: Serum CK (Creatine Kinase)
CK is the definitive diagnostic test for rhabdomyolysis.
- CK rises within the first 12 hours of muscle injury
- Peaks at 24-72 hours (first 3 days)
- Normalizes around day 5
- CK has a half-life of 1.5 days
- A CK level ≥5x the upper limit of normal (approximately ≥1,000 U/L), without another explanation, confirms the diagnosis
- Severe rhabdomyolysis often shows CK >10,000-100,000 U/L
"The definitive diagnosis of rhabdomyolysis is made by serologic testing for creatine kinase (CK)." - Rosen's Emergency Medicine
Supporting Tests
| Test | Finding in Rhabdomyolysis | Notes |
|---|---|---|
| Urine dipstick | Positive for blood, but few/no RBCs on microscopy | Myoglobin causes a false-positive blood result |
| Urine color | Tea-colored or dark brown | Indicates myoglobinuria (myoglobin >100-300 mg/L) |
| Serum myoglobin | Elevated (early) | Short half-life (1-3 hours) - unreliable; absence does NOT rule out rhabdo |
| Urine myoglobin | Elevated (early) | Also unreliable - clears quickly with good hydration |
| BMP/electrolytes | Hyperkalemia, hyperphosphatemia, early hypocalcemia | From muscle cell breakdown |
| BUN/Creatinine | Elevated | Monitors for acute kidney injury (AKI) |
| LFTs (AST, LDH) | Elevated | Muscle sources, not just liver |
| CBC | Variable | Baseline |
Key Clinical Pearl
The urine dipstick can be misleading - myoglobin triggers a false-positive blood result. The distinguishing feature is that the microscopic urinalysis shows few or no red blood cells, which tells you it's myoglobin (not hemoglobin or hematuria). Myoglobinuria + elevated CK together confirm the diagnosis.
CK is the only test you truly need - it's the most sensitive, stays elevated longest, and is the clinical gold standard for both diagnosis and monitoring treatment response.
(Rosen's Emergency Medicine; Tintinalli's Emergency Medicine; Comprehensive Clinical Nephrology, 7th Ed.)
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