A 4-year-old boy develops pallor and passage of dark red urine ten days after an upper respiratory infection. Hb 5.2 g/dL, LDH markedly raised, haptoglobin absent. Direct antiglobulin test is positive with C3d only, IgG and IgM negative. Incubating his serum with donor red cells at 4 degrees Celsius followed by warming to 37 degrees causes hemolysis. What is the diagnosis?
- A Paroxysmal cold hemoglobinuria due to the Donath Landsteiner antibody ✓
- B Cold agglutinin disease due to IgM antibodies
- C Warm autoimmune hemolytic anemia
- D Hemolytic uremic syndrome
Correct answer: A. Paroxysmal cold hemoglobinuria due to the Donath Landsteiner antibody
Explanation
Paroxysmal cold hemoglobinuria is caused by an IgG Donath Landsteiner biphasic hemolysin that binds red cells in cool peripheral circulation and fixes complement, with hemolysis occurring on rewarming to 37 degrees. It classically follows viral illness in children and produces abrupt intravascular hemolysis with hemoglobinuria and a Coombs test positive for C3d alone. Cold agglutinin disease is IgM mediated and usually chronic in adults, warm AIHA shows IgG positivity, and HUS features schistocytes and renal failure rather than complement positive hemolysis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.