1. Background

• exposure to a risk factor -> autoimmune phenomenon ->
  • enormous increase in IgM titres with IgM specificity of the I antigen on the RBC membrane -> formation of immune complex on RBC membrane -> activation of complement system with deposition of multiple C3B molecules on the RBC mem-brane activated RBC's attacked by macrophages containing specific receptors for C3B-coated cells -> phagocytosis

2. Risk Factors:

1. Anemia

• severe with pallor and/or jaundice
• complications:
  • see AUTOIMMUNE HEMOLYTIC ANEMIA-II
  • hemaglobinuria and hemaglobinemia upon exposure to cold
• two clinical patterns:
  • Acute Transient and Chronic Patterns
    • see AUTOIMMUNE HEMOLYTIC ANEMIA-II

1. Serum

• Hb: severe, normocytic, normochromic low or high reticulocytes +/- nucleated RBC's
• smear: agglutination, rouleaux formation
• hemolysis: increased free Hb and unconjugated bilirubin decreased haptoglobin and hemopexin
• leukocytosis with normal platelets
• positive direct Coombs test:
  • for IgM-coated RBC's
    • I antigen is altered in the cold (4 C) thus increasing its availability to IgM
    • IgM titre may increase to 1:30,000 (the dilution of antibody that can still agglutinate normal RBC's)
  • with animal antihuman anti-C3 reagent

2. Bone Marrow

• erythroid hyperplasia

3. Urinalysis

• hematuria, hemaglobinuria

1. Supportive

• hemodynamic compromise
  • PRBC transfusions
  • fluid resuscitation
• treat underlying disease
• avoid the cold

2. Medications

• Prednisone
  • tend to be less effective in this type of autoimmune HA

3. Others

• no role for splenectomy as IgM cleared by liver not spleen
• plasmaphoresis