Expected Urinalysis Findings in Trauma-Related Rhabdomyolysis
In this patient with rhabdomyolysis from severe trauma, the expected urinalysis finding is positive dipstick hemoglobin WITHOUT abundant RBCs in the urine sediment, along with proteinuria. 1, 2
Understanding the Diagnostic Pattern
The key to answering this question lies in understanding what happens when myoglobin enters the urine:
Dipstick testing will be positive for "blood" because standard urine dipsticks detect the heme moiety present in both hemoglobin AND myoglobin—they cannot distinguish between the two 1, 2
Microscopic examination shows few or NO red blood cells in the sediment, which is the critical distinguishing feature of myoglobinuria versus true hematuria 1, 2
Proteinuria is typically present (often 1-2+) because myoglobin itself registers as protein on dipstick testing 1, 2
The urine appears reddish-brown or tea-colored due to myoglobin pigment, not actual red blood cells 1, 3, 4
Why the Other Options Are Incorrect
Abundant RBCs in sediment would indicate true hematuria (bleeding into the urinary tract), not rhabdomyolysis. While this patient may have concurrent genitourinary trauma from the fall, the clinical scenario specifically asks about findings expected from rhabdomyolysis itself 1, 2
Isolated proteinuria without the positive dipstick hemoglobin would miss the pathognomonic finding—the dissociation between positive dipstick "blood" and absent/minimal RBCs on microscopy is what clinches the diagnosis of myoglobinuria 1, 2
Clinical Pearls and Pitfalls
The Classic Triad
The conventional presentation includes muscle pain, weakness, and dark urine, though not all patients manifest all three symptoms 4
Laboratory Confirmation
- Serum CK elevation (typically >5 times upper limit of normal, often >1,000 IU/L) is the biochemical gold standard for diagnosis 4, 5
- Serum myoglobin is the gold standard for prognostication, particularly in non-traumatic cases 4
- Urine myoglobin detected by qualitative dipstick was positive in only 19% of cases in one large series, so its absence does not exclude rhabdomyolysis 5
Critical Pitfall to Avoid
Do not rely on urine myoglobin testing alone—the qualitative dipstick/ultrafiltration method has poor sensitivity. The diagnosis rests on the clinical picture, elevated serum CK, and the characteristic urinalysis pattern of positive dipstick hemoglobin with minimal/absent RBCs 5
Immediate Management Priorities
Given this patient's severe trauma mechanism (7th floor fall), immediate priorities include 1, 6:
- Aggressive fluid resuscitation with isotonic saline (0.9% NaCl) starting immediately, targeting urine output ≥300 mL/hour 6
- Monitor for compartment syndrome (pain, tension, paresthesia, paresis are early signs) 1, 2
- Serial monitoring of CK, creatinine, and electrolytes (especially potassium) every 6-12 hours initially 1, 6
- Avoid potassium-containing fluids like Lactated Ringer's, as potassium levels can rise markedly after reperfusion 6