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Myoglobinuria is the presence of myoglobin in the urine, which usually results from rhabdomyolysis or muscle injury. [1] Myoglobin is present in muscle cells as a reserve of oxygen . Signs and symptoms
In addition to the myoglobinuria, two other mechanisms contribute to kidney impairment: low blood pressure leads to constriction of the blood vessels and therefore a relative lack of blood flow to the kidney, and finally uric acid may form crystals in the tubules of the kidneys, causing obstruction.
Although sufficient evidence is currently lacking, supplementation with a combination of sodium bicarbonate and mannitol is commonly utilized to prevent kidney failure in rhabdomyolysis patients. Sodium bicarbonate alkalizes urine to stop myoglobin from precipitating in renal tubules.
The myoglobin is filtered by the kidneys, but is toxic to the renal tubular epithelium and so may cause acute kidney injury. [32] It is not the myoglobin itself that is toxic (it is a protoxin), but the ferrihemate portion that is dissociated from myoglobin in acidic environments (e.g., acidic urine, lysosomes). [citation needed]
Characteristic signs and symptoms include rhabdomyolysis (breakdown of muscle fibers and subsequent release of myoglobin), myoglobinuria, recurrent muscle pain, and weakness. The myoglobin release causes the urine to be red or brown and is indicatory of damage being done to the kidneys which ultimately could result in kidney failure. [4]
Waxy casts are broad casts, which is a more general term to describe the wider cast product of a dilated duct, and are seen in chronic kidney failure. In nephrotic syndrome , many additional types of casts exist, including broad and waxy casts if the condition is chronic (this is referred to as a telescopic urine with the presence of many casts).