Autoimmune hemolytic anemia (AIHA) is mediated by antibodies, and in most cases immunoglobulin (Ig) G is the mediating antibody. This type of AIHA is referred to as "warm" AIHA because IgG antibodies bind best at body temperature. "Cold" AIHA is mediated by IgM antibodies, which bind maximally at temperatures below 37°C. AIHA caused by a drug reaction is rare, with an estimated annual incidence of 1:1,000,000 for severe drug-related AIHA.1 This article reviews the management of the more common types of AIHA, with a focus on warm, cold, and drug-induced AIHA; the evaluation and diagnosis of AIHA is reviewed in a separate article.
Warm Autoimmune Hemolytic Anemia
In AIHA, hemolysis is mediated by antibodies that bind to the surface of red blood cells. AIHA in which IgG antibodies are the offending antibodies is referred to as warm AIHA. “Warm” refers to the fact that the antibody binds best at body temperature (37°C). In warm AIHA, testing will show IgG molecules attached to the surface of the red cells, with 50% of patients also showing C3. Between 50% and 90% of AIHA cases are due to warm antibodies.2,3 The incidence of warm AIHA varies by series but is approximately 1 case per 100,000 patients per year; this form of hemolysis affects women more frequently than men.4,5
Steroids. The goal of therapy in warm AIHA can be hard to define. However, most would agree that a hematocrit above 30% (or higher to prevent symptoms) with a minimal increase in the reticulocyte count—reflective of a significantly slowed hemolytic process—is a reasonable goal. Initial management of warm AIHA is prednisone at a standard dose of 1 mg/kg daily (Table 1).6,7 Patients should be also started on proton-pump inhibitors to prevent ulcers. It can take up to 3 weeks for patients to respond to prednisone therapy. Once the patient’s hematocrit is above 30%, the prednisone is slowly tapered. Although approximately 80% of patients will respond to steroids, only 30% can be fully tapered off steroids. For patients who can be maintained on a daily steroid dose of 10 mg or less, steroids may be the most reasonable long-term therapy. In addition, because active hemolysis leads to an increased demand for folic acid, patients with warm AIHA are often prescribed folic acid 1 mg daily to prevent megaloblastic anemia due to folic acid deficiency.
Rituximab. Increasingly, rituximab (anti-CD20) therapy is added to the initial steroids. Two clinical trials showed both increased long-term and short-term responses with the use of rituximab.8,9 An important consideration is that most patients respond gradually to rituximab over weeks, so a rapid response should not be expected. Most studies have used the traditional dosing of 375 mg/m2 weekly for 4 weeks. These responses appear to be durable, but as in immune thrombocytopenia (ITP), repeat treatment with rituximab is effective.
The major side effects of rituximab are infusion reactions, which are often worse with the first dose. These reactions can be controlled with antihistamines, steroids, and, for severe rigors, meperidine. Rarely, patients can develop neutropenia (approximately 1:500) that appears to be autoimmune in nature. Infections appear to be only minimally increased with the use of rituximab.10 One group at risk is chronic carriers of hepatitis B virus, who may experience a reactivation of the virus that can be fatal. Thus, patients being considered for rituximab need to be screened for hepatitis B virus carrier state.11 Patients receiving rituximab are at very slight risk for progressive multifocal leukoencephalopathy, which is more common in patients with cancer and in heavily immunosuppressed patients. The overall risk is unknown but is less than 1:50,000.