Urine Changes in Rhabdomyolysis
Primary Urine Finding
The hallmark urine change in rhabdomyolysis is myoglobinuria, which manifests as dark brown or tea-colored urine that tests positive for blood on dipstick without visible red blood cells on microscopy. 1, 2
Key Urinalysis Findings
Urine appears brown, dark, or tea-colored due to the presence of myoglobin released from damaged muscle tissue 1, 2
Dipstick testing shows positive for blood (heme) without red blood cells present on microscopic examination - this is the classic diagnostic pattern that distinguishes myoglobinuria from hematuria 1
The urine cloudiness may be present alongside the brown discoloration 1
Important Clinical Context
Myoglobinuria may be absent in up to 81% of rhabdomyolysis cases when detected by qualitative dipstick/ultrafiltration methods, so the absence of visible myoglobin does not exclude the diagnosis 3
Serum myoglobin has a short half-life and is released earlier than creatine kinase (CK), making it detectable in urine before CK peaks 4
The conventional clinical triad includes muscle pain, weakness, and dark urine, though not all patients present with all three symptoms 2
Diagnostic Approach
When urine shows positive dipstick for blood without RBCs on microscopy, immediately measure serum CK - a level >5 times the upper limit of normal (>975 IU/L) or >10 times normal confirms rhabdomyolysis 3, 5
Monitor urine output closely with goal of maintaining >300 mL/hour through aggressive fluid resuscitation to prevent acute kidney injury 5
Maintain urine pH at approximately 6.5 if possible through alkalinization strategies 6
Critical Pitfall
The most important caveat is that qualitative urine myoglobin testing has poor sensitivity (only 19% positive in confirmed cases), so clinicians must not rely on urine findings alone and should always measure serum CK when rhabdomyolysis is suspected 3. The absence of dark urine or negative urine myoglobin does not exclude rhabdomyolysis.