Immune-mediated thrombocytopenia (IMT) is a relatively common cause of bleeding in small animals, particularly the dog. Many differing disease processes may initiate IMT Despite heterogenous aetiologies, most cases of IMT share common pathophysiological features: high levels of platelet-associated antibody, enhanced platelet destruction by the mononuclear phagocytic system (MPS), and markedly decreased circulating platelet life-span. Thrombocytopenia develops when platelet destruction exceeds compensatory platelet production by marrow megakaryocytes.