Warm autoimmune hemolytic anemia ( WAIHA)
• RBCs are coated with IgG and/ or complement. Macrophages may phagocytize these RBCs, or they may remove the antibody or complement from the RBC's surface, causing membrane loss and spherocytes.
• 60% of cases are idiopathic; other cases are secondary to diseases that alter the immune response ( e. g., chronic lymphocytic leukemia, lymphoma); can also be drug induced.
• Laboratory: Spherocytes, MCHC may be 37 g/ dL, increased osmotic fragility, bilirubin, reticulocyte count; occasional nRBCs present; positive direct antiglobulin test ( DAT) helpful in differentiating from hereditary spherocytosis.
Cold autoimmune hemolytic anemia ( CAIHA or cold hemagglutinin disease)
• RBCs are coated with IgM and complement at temperatures below 37° C. RBCs are lysed by complement or phagocytized by macrophages. Antibody is usually anti- I but can be anti- i.
• Can be idiopathic, or secondary to Mycoplasma pneumoniae, lymphoma, or infectious mononucleosis
• Laboratory: Seasonal symptoms; RBC clumping can be seen both macroscopically and microscopically; MCHC 37 g/ dL; increased bilirubin, reticulocyte count; positive DAT detects complement- coated RBCs
• If antibody titer is high enough, sample must be warmed to 37° C to obtain accurate RBC and indices results.
Paroxysmal cold hemoglobinuria ( PCH)
• An IgG biphasic Donath- Landsteiner antibody with P specificity fixes complement to RBCs in the cold ( less than 20° C); the complement- coated RBCs lyse when warmed to 37° C.
• Can be idiopathic, or secondary to viral infections ( e. g., measles, mumps) and non- Hodgkin lymphoma
• Laboratory: Variable anemia following hemolytic process; increased bilirubin and plasma hemoglobin, decreased haptoglobin; DAT may be positive; Donath- Landsteiner test positive