A 68-year-old man with a metallic mitral valve replacement is found to have Hb 8.4 g/dL, reticulocyte count 6 percent, undetectable haptoglobin, and LDH of 1200 U/L. The peripheral smear shows fragmented red cells. What is the predominant route of red cell destruction in this condition?

• A Mechanical fragmentation of red cells by turbulent shear stress ✓
• B Complement mediated intravascular lysis
• C Extravascular hemolysis mediated by IgG-coated cells in the spleen
• D Splenic sequestration of rigid spherocytes

Explanation

Prosthetic valve hemolysis is a form of microangiopathic hemolytic anemia in which turbulent, high-shear flow across the valve physically shears red cells, producing schistocytes. Destruction is intravascular, releasing free hemoglobin, depleting haptoglobin, and raising LDH, but the mechanism is mechanical trauma, not immune attack. Complement lysis applies to PNH and cold antibody syndromes, and IgG-mediated splenic removal applies to warm autoimmune hemolysis and hereditary spherocytosis, none of which produce schistocytes.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.