Immune Haemolytic Anaemia

Abstract The immune haemolytic anaemias comprise a set of diseases characterised by shortened red blood cell survival (haemolysis) mediated by the action of antibodies and serum complement. The haemolysis is evidenced by a raised reticulocyte count in the absence of blood loss. Activity of the immune system is diagnosed by the presence of antibody or fragments of complement components (mainly C3 and C4) on the red blood cell surfaces by means of the direct antiglobulin test. Pathogenic antibodies may bind optimally at either 37°C (warm autoimmune haemolytic anaemia) or at 4°C (cold agglutinin disease). Drugs may also cause immune haemolysis either by induction of drug‐dependent antibodies to red blood cells or by induction of autoantibodies. Key Concepts: The immune haemolytic anaemias are characterised by shortened red blood cell survival mediated by the action of antibodies and complement. The key laboratory finding is the demonstration of antibody or complement on red blood cells by means of the direct antiglobulin (Coombs) test. Antibodies may bind optimally at body temperature (37°C; warm antibody autoimmune haemolytic anaemia) or at 4°C (cold agglutinin disease). Autoimmune haemolytic anaemia is most often idiopathic, but some cases occur in association with other diseases, most commonly a lymphoma or systemic lupus erythematosus. Drugs may cause antibody binding to red blood cells by three distinct mechanisms. Nowadays, the most common offending drugs are second and third generation cephalosporins. Treatment options include glucocorticoids and splenectomy (warm antibody autoimmune hemolysis); rituximab (warm antibody autoimmune haemolysis and cold agglutinin disease); and removal of the offending drug (drug‐immune haemolytic anaemia). Transfusion should not be withheld from patients with symptomatic anaemia while awaiting a response to other treatments.