<unk>  can be caused by a number of different classes of antibody, with IgG and IgM antibodies being the main causative classes. Depending on which is involved, the pathology will differ. IgG is not very effective at activating complement and effectively binds the Fc receptor (FcR) of phagocytic cells,<unk>  involving IgG is generally characterized by phagocytosis of RBCs. IgM is a potent activator of the classical complement pathway, thus,<unk>  involving IgM is characterized by complement-mediated lysis of RBCs. IgM also leads to phagocytosis of RBCs however, because phagocytic cells have receptors for the bound complement (rather than FcRs as in IgG<unk> . In general, IgG<unk>  takes place in the spleen, whereas IgM<unk>  takes place in Kupffer cells – phagocytic cells of the liver. Phagocytic<unk>  is termed extravascular, whereas complement-mediated lysis of RBCs is termed intravascular<unk> . In order for intravascular<unk>  to be recognizable, it requires overwhelming complement activation, therefore most<unk>  is extravascular – be it IgG- or IgM-mediated.<unk>  cannot be attributed to any single autoantibody. To determine the autoantibody or autoantibodies present in a patient, the Coombs test, also known as the antiglobulin test, is performed. There are two types of Coombs tests, direct and indirect; more commonly, the direct antiglobulin test (DAT) is used. Classification of the antibodies is based on their activity at different temperatures and their etiology. Antibodies with high activity at physiological temperature (approximately 37 °C) are termed warm autoantibodies. Cold autoantibodies act best at temperatures of 0–4 °C. Patients with cold-type<unk> , therefore, have higher disease activity when body temperature falls into a hypothermic state. Usually, the antibody becomes active when it reaches the limbs, at which point it opsonizes RBCs. When these RBCs return to central regions, they are damaged by complement. Patients may present with one or both types of autoantibodies; if both are present, the disease is termed "mixed-type"<unk> . When DAT is performed, the typical presentations of<unk>  are as follows. Warm-type<unk>  shows a positive reaction with antisera to IgG antibodies with or without complement activation. Cases may also arise with complement alone or with IgA, IgM or a combination of these three antibody classes and complement. Cold-type<unk>  usually reacts with antisera to complement and occasionally to the above antibodies. This is the case in both cold agglutinin disease and cold paroxysmal hematuria. In general, mixed warm and cold<unk>  shows a positive reaction to IgG and complement, sometimes IgG alone, and sometimes complement alone. Mixed-type can, like the others, present unusually with positive reactions to other antisera.
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