Mahogany or brown urine

Specialty: Nephrology and urology.

• tea-colored urine or car cola
• dark brown non-hematic urine
• myoglobinuria or macroscopic hemoglobinuria

Why it occurs

• Myoglobinuria due to severe rhabdomyolysis (massive destruction of skeletal muscle due to crush trauma, extreme strenuous exercise, muscle ischemia, prolonged seizures or use of statins, releasing myoglobin that stains the urine and is highly nephrotoxic)
• Hemoglobinuria due to massive intravascular hemolysis (acute hemolytic transfusion reactions, microangiopathic hemolytic anemia or infections such as severe Plasmodium falciparum malaria, releasing filterable free hemoglobin)
• Alkaptonuria (rare metabolic disease where the excreted homogentisic acid is oxidized upon contact with air, staining the urine dark brown)
• Porphyria cutanea Tarda (accumulation of porphyrins that stain urine a port wine or mahogany color after exposure to sunlight)
• Intoxication by phenols or medications (such as metronidazole, nitrofurantoin or methocarbamol, whose metabolites temporarily stain urine dark)
• Extreme dehydration (maximum concentration of urochrome pigments and amorphous urates)

Initial workup

Urine dipstick (will read positive for "blood/hemoglobin" due to the peroxidase activity of myoglobin and free hemoglobin); microscopic examination of the urinary sediment to confirm the absence of erythrocytes (if the strip is positive but there are no erythrocytes, myoglobinuria or hemoglobinuria is confirmed); serum Creatine Phosphokinase (CPK) quantification (elevated >5 times the upper limit in rhabdomyolysis); complete blood count with peripheral blood smear (search for schistocytes), serum haptoglobin, lactate dehydrogenase (LDH), and free and conjugated bilirubins.

Standard management

• 0.9% isotonic saline solution — early aggressive intravenous fluid therapy at a rate of 200-300 ml/h to force a diuresis of at least 200 ml/h, reducing precipitation and tubular toxicity of myoglobin and hemoglobin in the collecting ducts
• 1.4% baking soda — in intravenous infusion to alkalinize urine to a pH >6.5, which increases the solubility of myoglobin and prevents the formation of destructive intratubular acid casts; discontinue if systemic alkalosis or hypocalcemia is present
• Furosemide (20-40 mg IV if strictly necessary to force diuresis in case massive fluid therapy causes signs of volume overload in a patient with depressed cardiac function).