myoglobinuric

Myoglobinuric is an adjective used to describe conditions in which myoglobin appears in the urine, most often as a consequence of muscle injury such as rhabdomyolysis. The term is frequently associated with myoglobinuric nephrosis, a form of acute kidney injury thought to result from the toxic effects of myoglobin on renal tubules and from tubular obstruction.

Pathophysiology and presentation

When skeletal muscle is damaged, myoglobin is released into the bloodstream and filtered by the kidneys. Myoglobin in the renal tubules can cause direct oxidative injury and can precipitate as casts, contributing to tubular obstruction. Clinically, myoglobinuric disorders often present with dark or cola-colored urine, muscle pain or weakness, and signs of systemic illness depending on the underlying cause. Complications may include electrolyte disturbances and, in severe cases, acute kidney injury.

Diagnosis

Urinalysis may show a positive test for blood on dipstick without a proportionate number of red blood cells on microscopy, reflecting the presence of myoglobin. Serum creatine kinase is typically markedly elevated. Myoglobin levels can be measured but are not routinely required in all settings. Renal function tests may reveal elevated creatinine and may be accompanied by electrolyte abnormalities, especially hyperkalemia.

Management

Treatment centers on addressing the underlying cause of muscle injury and maintaining renal perfusion. Aggressive intravenous fluid administration is standard to sustain urine output. Electrolyte abnormalities should be monitored and corrected. The role of urine alkalinization with bicarbonate is debated and not universally recommended. Dialysis may be necessary for patients with severe acute kidney injury, refractory electrolyte disturbances, or volume overload.

See also

Rhabdomyolysis, myoglobinuria, acute kidney injury.