Autoimmune hemolytic anemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Assosciate Editor(s)-In-Chief: Prashanth Saddala M.B.B.S; Shyam Patel [2]
Overview
Autoimmune hemolytic anemia is a type of hemolytic anemia where the body's immune system attacks its own red blood cells, leading to their destruction (hemolysis). Antibodies and associated complement system components become fixed onto the red blood cell surface. These antibodies can be detected with the Coombs test or direct Coombs test. Autoimmune hemolytic anemia can also be induced by infections such as Mycoplasma pneumoniae, drugs such as methyldopa and fludarabine, or malignancies such as chronic lymphocytic leukemia or non-Hodgkin lymphoma.
Historical Perspective
The history of studies on autoimmune hemolytic anemia begins in the early 20th century with the description of clinical syndromes involving low hemoglobin in the setting of a circulating antibody. Various groups reported on the production of antibodies that could bind to red blood cells at either warm or cold temperatures. Over the years, diagnostic tests were developed and optimized to determine the exact type of antibody involved in hemolysis. Treatment modalities were developed, beginning with corticosteroids. Other immunosuppressive medications, such as rituximab, were soon found to be effective in patients with hemolytic anemia.
Classification
Autoimmune hemolytic anemia is classified into 3 broad categories. These include warm-antibody type, cold-antibody type, and mixed-antibody type. Each category is characterized by a different autoantibody (IgG or IgM) and different optimal binding temperatures (37 degrees Celsius or 4-18 degrees Celsius). Each condition is associated with different triggers, including infections, medications, and malignancies. The warm-antibody type is the most common, and the mixed-antibody type is rare and not well characterized.
Pathophysiology
The pathophysiology of autoimmune hemolytic anemia is different for warm-antibody type and cold-antibody type anemia. The pathophysiology of warm-antibody type autoimmune hemolytic anemia involves the coating of red blood cells with IgG, followed by extravascular hemolysis by splenic macrophages. The pathophysiology of cold-antibody type autoimmune hemolytic anemia involves the coating of red blood cells with IgM, followed by intravascular hemolysis. The complement system has a significant role in autoimmune hemolytic anemia and involves the binding of classical complement proteins on the red blood cell surface, followed by cell lysis by the membrane attack complex. In summary, a variety of cell-mediated immunologic mechanisms underlie the pathophysiology of autoimmune hemolytic anemia.
Causes
Autoimmune hemolytic anemia is caused by primary and secondary conditions. Secondary conditions that cause autoimmune hemolytic anemia include malignancies, autoimmunity, and medications. Malignancies that cause autoimmune hemolytic anemia include chronic lymphocytic leukemia and non-Hodgkin lymphoma. Autoimmune conditions that cause autoimmune hemolytic anemia include systemic lupus erythematosus, primary biliary cirrhosis, and others. Medications that cause autoimmune hemolytic anemia include methyldopa and fludarabine.
Differentiating Autoimmune Hemolytic Anemia from Other Diseases
A variety of conditions comprise the differential diagnosis of autoimmune hemolytic anemia. These include microangiopathic hemolytic anemia, paroxysmal cold hemoglobinuria, paroxysmal nocturnal hemoglobinuria, hereditary spherocytosis, pernicious anemia, and chronic lymphocytic leukemia. The diagnosis of autoimmune hemolytic anemia can sometimes be made by first ruling out these other causes. It is important to distinguish amongst these conditions since the prognosis and treatment of each condition is different.
Epidemiology and Demographics
Overall, the incidence and prevalence of autoimmune hemolytic anemia is low. This condition affects a very small proportion of the population. Autoimmune hemolytic anemia affects men and women equally. There is no racial predilection for autoimmune hemolytic anemia.
Risk Factors
The risk factors for autoimmune hemolytic anemia include systemic lupus erythematosus and immunotherapeutic medications. Systemic lupus erythematosus is thought to be a strong risk factor for autoimmune hemolytic anemia. However, immunotherapeutic medications may become a more prevalent risk factor in the coming years as these agents are becoming used increasingly for a variety of cancers. These medications include anti-PD-1 antibodies and anti-CTLA-4 antibodies.