This patient's presentation is most consistent with rhabdomyolysis. Myoglobinuria commonly occurs in rhabdomyolysis and presents with blood detected on dipstick urinalysis without RBCs seen on urine microscopy.
Rhabdomyolysis is the acute breakdown of skeletal muscle with subsequent leakage of muscle contents into the circulation. Most notable of these contents is myoglobin, which may cause irreversible renal damage by precipitating in the glomerulus. Urine dipsticks are sensitive for detecting the heme protein; however, they do not differentiate between hemoglobin, myoglobin, and actual RBCs. Myoglobin breaks down to byproducts including heme protein; therefore, the presence of substantial myoglobin in the urine will lead to a positive blood dipstick urinalysis but no RBCs will be visible on microscopy. Urine myoglobin levels may also be obtained to confirm the diagnosis in the event of a positive dipstick and a negative microscopy.
Sauret et al. review the presentation, diagnosis, and management of rhabdomyolysis. Causes of rhabdomyolysis are numerous and may include crush injury, overexertion, alcohol abuse, or genetic syndromes (McArdle's disease or Duchenne's muscular dystrophy). Early complications of rhabdomyolysis can include hyperkalemia leading to cardiac arrhythmia/arrest. The most serious late complication is acute renal failure.
Zimmerman et al. discuss the management of rhabdomyolysis, particularly stopping ongoing muscle damage, preventing the development of acute renal failure, and mitigating the risk of other fatal complications (such as calcium gluconate to stabilize cardiac membranes in the setting of hyperkalemia). Aggressive and prompt fluid resuscitation to increase perfusion of the kidneys and improve urine output remains the mainstay treatment for preventing and managing acute kidney injury. Other treatment options are supplementary and may include bicarbonate, mannitol, and loop diuretics.
Figure A is an EKG demonstrating peaked T waves, consistent with the hyperkalemia that accompanies rhabdomyolysis. Illustration A summarizes the differing findings between rhabdomyolysis, hematuria, and hemolysis. Illustration B depicts the pathophysiology of rhabdomyolysis; note obstruction and ischemic injury to the tubules.
Answer 1: A normal dipstick would not be expected in myoglobinuria.
Answer 2: Neither a normal dipstick nor positive blood on urine microscopy would be expected with the myoglobinuria associated with rhabdomyolysis.
Answer 3: These findings are consistent with hematuria, not myoglobinuria.
Answer 5: These findings of positive leukocytes and nitrite as well as numerous WBCs on microscopy is more consistent with a urinary tract infection.
Sauret JM, Marinides G, Wang GK. Rhabdomyolysis. Am Fam Physician. 2002 Mar 1;65(5):907-12.
PMID:11898964 (Link to Abstract)
Zimmerman JL, Shen MC. Rhabdomyolysis. Chest. 2013 Sep;144(3):1058-65. doi: 10.1378/chest.12-2016.
PMID:24008958 (Link to Abstract)