Chapter 16 Autoimmune Hemolytic Anemia
Figure 16-1 MECHANISM OF EXTRAVASCULAR HEMOLYSIS IN AUTOIMMUNE HEMOLYTIC ANEMIA.
A, Macrophage encounters an IgG-coated erythrocyte and binds to it via its Fc receptors. Thus entrapped, the red blood cell (RBC) loses bits of its membrane as a result of digestion by the macrophage’s ectoenzymes. The discoid erythrocyte transforms into a sphere. B, RBC lightly coated with IgG (and therefore incapable of activating the complement cascade) is preferentially removed in the sluggish circulation of the spleen. C, RBC with a heavy coat of IgG; thus, C3b (black circles) can be removed both by the spleen and the liver.
(From Cunnigham MJ, Silberstein LE: Autoimmune Hemolytic Anemia. In Hoffman R, Benz EJ Jr, Shattil SJ, et al, eds: Hematology: Basic principles and practice, ed 4, 2005, Philadelphia, Elsevier.)
CAIHA, Cold autoimmune hemolytic anemia; Ig, immunoglobulin; WAIHA, warm autoimmune hemolytic anemia.
Four Important Questions for the Diagnosis and Management of Autoimmune Hemolytic Anemia
It is of utmost importance to differentiate between various types of AIHA. A stepwise approach helps in making the right decisions:
Question 1: Hemolytic anemia? The basic features of hemolytic anemia are reticulocytosis, low haptoglobin levels, elevated indirect bilirubin, and elevated LDH.
Question 2: Autoimmune hemolytic anemia? A direct DAT is initially performed with a polyspecific antibody to detect IgG or complement C3d bound to RBCs. If the DAT result is positive, the diagnosis of AIHA is established.