Cold agglutinins are normally made by the immune system in response to infection and cause red blood cells to clump together (agglutinate) at low temperatures.
In primary autoimmune hemolytic anemia, no underlying systemic disease explains the presence of autoantibodies, whereas secondary autoimmune hemolytic anemia results from a systemic disease. The autoantibody may be Immunoglobulin G (IgG), Immunoglobulin M (IgM), or, rarely, Immunoglobulin A (IgA); it may be warm reacting or cold reacting.
Secondary cold agglutinin disease is usually caused by infection and lymphoproliferative disorders. Monoclonal secondary disease is usually chronic, occurring in adults. Polyclonal secondary cold agglutinin disease, which occurs in children and young adults, is usually transient.
Prognosis of the disease may be associated with an excellent long-term prognosis when secondary to M pneumonia or viral infections. In children and young adults, the condition usually lasts 1-3 weeks; evidence of cold agglutinins disappears within 6 months.
Patients with the mildly to moderately severe primary (idiopathic) variety of cold agglutinin disease are expected to have a good long-term prognosis if excessive exposure to cold is avoided and with close medical surveillance for complications or progression to lymphoma.
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