The causes of<unk>  are poorly understood. The disease may be primary, or secondary to another underlying illness. The primary illness is idiopathic (the two terms used synonymously). Primary<unk>  accounts for more than 60% of unselected cases. Secondary<unk>  can result from many other illnesses. Warm and cold type<unk>  each have their own more common secondary causes. The most common causes of secondary warm-type<unk>  include lymphoproliferative disorders (e.g., chronic lymphocytic leukemia, lymphoma) and other autoimmune disorders (e.g., systemic lupus erythematosus, rheumatoid arthritis, scleroderma, Crohn's disease, ulcerative colitis). Less common causes of warm-type<unk>  include neoplasms other than lymphoid, and infection. Secondary warm type<unk>  has been observed in cases of Covid-19. Secondary cold type<unk>  is also caused primarily by lymphoproliferative disorders but is also commonly caused by infection, especially by mycoplasma, viral pneumonia, infectious mononucleosis, and other respiratory infections. Less commonly, it can be caused by concomitant autoimmune disorders. Drug-induced<unk> , though rare, can be caused by a number of drugs, including α-methyldopa and penicillin. This is a type II immune response in which the drug binds to macromolecules on the surface of the RBCs and acts as an antigen. Antibodies are produced against the RBCs, which leads to complement activation. Complement fragments, such as C3a, C4a and C5a, activate granular leukocytes (e.g., neutrophils), while other components of the system (C6, C7, C8, C9) either can form the membrane attack complex (MAC) or can bind the antibody, aiding phagocytosis by macrophages (C3b). This is one type of "penicillin allergy". In about half of cases, the cause of<unk>  cannot be determined (idiopathic or primary). This condition can also be caused by or occur with another disorder (secondary) or rarely, occur following the use of certain drugs (such as penicillin) or after a person has a blood and marrow stem cell transplant. Secondary causes of<unk>  include: * Autoimmune diseases, such as lupus * Chronic lymphocytic leukemia * Non-Hodgkin's lymphoma and other blood cancers * Epstein-Barr virus * Cytomegalovirus * Mycoplasma pneumonia * Hepatitis * HIV
Autoimmune hemolytic anemia
Mixed autoimmune hemolytic anemia
Cold autoimmune hemolytic anemia
Acquired hemolytic anemia
Microangiopathic hemolytic anemia
Mechanical hemolytic anemia
Drug-induced nonautoimmune hemolytic anemia
Cryoglobulinemia