A 58-year-old man with a mechanical mitral valve replacement has stable hemoglobin of 9.6 g/dL, reticulocytes 6%, LDH 900 U/L, undetectable haptoglobin, and dark brown urine. Peripheral smear shows fragmented red cells and polychromasia. What is the underlying cause of his anemia?

• A Shear stress fragmentation of red cells across the prosthetic valve surface ✓
• B Oxidant induced precipitation of hemoglobin with Heinz body formation
• C Autoimmune spherocyte formation followed by splenic sequestration
• D Defective assembly of GPI anchored complement regulators on red cells

Explanation

Mechanical valves can shear red cells passing through, producing microangiopathic hemolysis with schistocytes, high LDH, low haptoglobin, and chronic hemosiderinuria, often requiring iron and sometimes folate supplementation. Spherocytes point toward autoimmune or hereditary spherocytosis rather than fragmentation, ruling out option C. Absent CD55 and CD59 defines paroxysmal nocturnal hemoglobinuria, which also causes dark urine, making option D a strong distractor, but the schistocytes with a valve prosthesis decide the answer.

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.