Table 1 provides a comparison of the key characteristics between Warm Autoimmune Hemolytic Anemia (AIHA) and Cold AIHA. Blood bank testing will differentiate which type of AIHA is occurring starting with the DAT.
Autoantibodies can cause issues in blood bank workups including ABO typing and antibody screens at all temperature phases. It is important that any unexplained agglutination is worked up and alloantibodies identified prior to transfusion. Follow your institution's policies and recommendations for positive antibody screens.
Table 1. Warm AIHA vs. Cold AIHA.
| Warm AIHA | Cold AIHA |
| Optimal Temperature for Reactivity | 37ºC | 4ºC |
| Autoantibody | IgG | IgM |
| Autoantibody Specificity | Rh system | Ii system
(P in PCH) |
| Complement Activation | Low-titer or None | Yes |
| DAT (Direct Coombs) | IgG positive
C3 positive or negative | IgG negative
C3 positive |
| Eluate | Pan-reactive | Non-reactive |
| Peripheral Smear | Spherocytes | Rouleaux / Agglutination |
| Primary Site of Hemolysis | Extravascular | Intravascular |
