Pediatric emergency medicine trisk 2192 2192

of antibodies on erythrocytes and is usually positive in AIHA. A positive DAT prompts
additional testing by the blood bank to further characterize the antibody. Acute
hemolysis is most commonly associated with a warm (37°C)-reactive IgG antibody with
or without complement (C3). This type of hemolysis is usually extravascular, occurring
in the spleen. IgM-mediated cold agglutinin disease is less common in children than in
adults, but can occur following mycoplasma (anti-I) or infectious mononucleosis (antii). These antibodies bind to RBCs in the cold and characteristically cause intravascular
hemolysis as complement is bound and activated at warmer temperatures. Cold-reactive
IgG antibodies (Donath–Landsteiner test) cause paroxysmal cold hemoglobinuria
(PCH), which in children frequently follows a viral infection. A negative DAT does not
definitively exclude an immune-mediated process. Rarely, IgA or warm–reactive-IgM
antibodies may be present but not detected by the Coombs reagent. Additionally, in rare
cases, the causative warm-IgG antibodies are below the level of detection. When there is
a high degree of suspicion for an immune-mediated process despite a negative DAT,
specialized assays are required for antibody detection.