ABSTRACT
Acquired: autoimmune hemolytic anemia, transfusion mismatch, traumatic (e.g., prosthetic valve as in this case, march hemoglobulinuria), thermal injury, infection (e.g., malaria)
• Serum hemoglobin binds to haptoglobin. When the haptoglobin levels decrease, the free hemoglobin (methemoglobin) is cleared by the kidneys
• Serum free hemoglobin concentration must exceed at least 25 mg/100 mL before hemoglobinuria ensues
• Urine dipstick test is positive for heme in both myoglobinuria and hemoglobinuria, but only in hemoglobinuria is the serum plasma pink-red. This occurs because haptoglobin binds hemoglobin as opposed to myoglobin
• In patients with a mechanical valve prosthesis, perivalvular leakage, even if hemodynamically insignificant, can induce hemolysis. The irregular valvular contour may generate enough shear stress to damage erythrocytes
• In cases of traumatic hemolysis due to valve replacements, reoperation is often necessary and may lead to immediate reversal of the hemolysis and consequent resolution of hemoglobinuria
