A 26-year-old man reports morning reddish urine that clears during the day, recurrent abdominal pain, and one episode of portal vein thrombosis. Flow cytometry of his granulocytes shows absent expression of two glycosylphosphatidylinositol anchored proteins. Which pair was tested?

• A CD4 and CD8
• B CD55 and CD59 ✓
• C CD16 and CD56
• D CD34 and CD117

Explanation

Paroxysmal nocturnal hemoglobinuria arises from an acquired PIGA mutation in a hematopoietic stem cell, preventing synthesis of GPI anchors. Decay accelerating factor CD55 and membrane attack complex inhibitor CD59 are GPI anchored, so their loss leaves red cells susceptible to complement lysis, explaining intravascular hemolysis and thrombophilia. Flow cytometric demonstration of deficient CD55 and CD59 on granulocytes is the current diagnostic standard, replacing the acidified serum lysis test.

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.