Patterns of direct antiglobulin (direct Coombs) test in autoimmune hemolytic anemias

Type of hemolysis	Pattern of positivity	Antigen	Comments
Warm AIHA	Anti-IgG and/or anti-C3	Rh complex antigens or glycoprotein antigens	Usually IgG (rarely IgA or IgM); typically panagglutinins
Drug-induced AIHA	Anti-IgG and/or anti-C3	Drug plus RBC antigen or Rh complex	Usually IgG (rarely IgM)
Cold agglutinin disease	Anti-C3	I or i antigen	IgM; agglutinates RBCs
Paroxysmal cold hemoglobinuria	Anti-C3	P antigen	IgG; fixes complement in the cold; hemolysis occurs when the sample is warmed (Donath-Landsteiner antibody)

Refer to UpToDate for the evaluation and diagnosis of hemolytic anemias.

AIHA: autoimmune hemolytic anemia; Ig: immunoglobulin; C3: third component of complement; RBCs: red blood cells.

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