Acquired Forms of Hemolysis

The acquired forms of reticuloendothelial or extravascular hemolysis are dominated by patients with acquired immunemediated hemolytic disease. Patients with autoimmune hemolytic anemia (AHA) can present with severe anemia; this is usually associated with another disease such as a collagen vascular disease (e.g., rheumatoid arthritis, severe systemic lupus erythematosus) or drugs, or it is idiopathic. AHA is uncommon but can be dramatic on presentation. About 50% of patients have no associated disease. The Coombs antiglobulin test, performed directly and indirectly determines the presence of antibody coating the patient's RBCs or free antibody in the plasma capable of binding to RBCs in AHA diagnosis. The autoantibodies may fix complement or may target the red cell for phagocytosis by the RES.

Therapy of AHA depends on the severity and causative mechanism. If the AHA is drug-induced, it is often sufficient to stop the drug and wait for the antibodies to clear, although this may take some time. Drug-induced hemolytic disease is uncommon and requires a specialized laboratory to make a precise diagnosis. AHA associated with collagen vascular diseases, lymphomas, or Hodgkin's disease may be controlled with treatment of the primary underlying condition. The mainstay of treatment of AHA is high-dose corticoste-roid therapy, at least 1 mg/kg of prednisone daily; refractory cases may require up to 2 mg/kg/day. Patients who do not respond to steroid therapy may be candidates for splenec-tomy, because the spleen is the primary site of removal of antibody-coated RBCs. Other drugs used as second- and third-line therapies for their immunosuppressive effects include cyclophosphamide, chlorambucil, and intravenous immune globulin (IVIG).

A final mechanism of acquired extravascular hemolysis is hypersplenism. Typically, patients with hypersplenism have an enlarged spleen because of infiltrative disease of the spleen, or they have splenomegaly as a result of portal hypertension. Under these circumstances, the RBCs are trapped for an unusually long period in the splenic circulation. Splenec-tomy may be beneficial.

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