A 5-year-old boy develops sudden pallor and gross hemoglobinuria one week after a viral upper respiratory infection. Direct antiglobulin test is positive for complement only. The antibody most likely targets which antigen?

• A Rh protein complex
• B Kell antigen
• C I/i antigen
• D P antigen ✓

Explanation

Paroxysmal cold hemoglobinuria is caused by the Donath-Landsteiner antibody, an IgG antibody that binds the P antigen on red cells at low temperature and fixes complement, causing intravascular hemolysis on rewarming. It classically affects children after viral infections and produces a biphasic hemolysin pattern. Anti-I/i IgM antibodies cause cold agglutinin disease seen in mycoplasma infection and EBV, while Rh and Kell specificities characterize warm AIHA and alloimmune reactions respectively.

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.