A 58-year-old woman reports fatigue and bluish discoloration of her earlobes and nose tip in cold weather, resolving indoors. Hb 8.1 g/dL, MCV 112 fL, but the analyzer flag notes red cell aggregates; repeating the CBC on a prewarmed sample gives MCV 94 fL. Smear shows clumped red cells. Direct antiglobulin test is positive for C3 only, negative for IgG. What is the diagnosis?
- A Cold agglutinin disease caused by IgM antibodies with a restricted thermal amplitude ✓
- B Warm autoimmune hemolytic anemia with complement activation
- C Paroxysmal cold hemoglobinuria caused by the Donath-Landsteiner antibody
- D Type II mixed cryoglobulinemia
Correct answer: A. Cold agglutinin disease caused by IgM antibodies with a restricted thermal amplitude
Explanation
Chronic cold agglutinin disease features IgM pentamers binding below 32 degrees Celsius, fixing complement on red cells. Acrocyanosis, spurious macrocytosis from agglutination that corrects on warming the sample, and a DAT positive only for C3 are characteristic. Warm AIHA shows IgG on the DAT, and Donath-Landsteiner antibody causes episodic hemoglobinuria in children after viral illness rather than chronic acrocyanosis with a corrected MCV.
Reference: Williams Hematology, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.