An 68-year-old woman with a bileaflet mechanical mitral valve replacement presents with slowly worsening anemia, Hb 8.5 g/dL, LDH 900 IU/L, and undetectable haptoglobin. Smear shows fragmented cells. Direct antiglobulin test is negative. What is the primary mechanism?
- A Warm-reactive IgG opsonization of red cells
- B Complement-mediated intravascular lysis by cryoglobulins
- C Shear stress fragmentation of red cells across the prosthesis ✓
- D Splenic sequestration of rigid spherocytes
Correct answer: C. Shear stress fragmentation of red cells across the prosthesis
Explanation
Mechanical valves generate turbulent, high-shear flow that physically fragments red cells, producing schistocytes, intravascular hemolysis, elevated LDH, and low haptoglobin. The negative direct antiglobulin test excludes immune hemolysis, and no spherocytes are formed because there is no antibody-mediated membrane loss. This is a form of microangiopathic-type hemolytic anemia arising from a structural cardiovascular source rather than fibrin strands in small vessels.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.