A large platelet is a platelet that is more than 10 μm in diameter and has an average volume of more than 11 fL. An elevated number of large platelets often indicates the presence of immature platelets in the peripheral blood. Large platelets are usually immature platelets, while developed mature platelets are usually smaller in size. An increased number of large platelets often represents a disease, which is immune thrombocytopenic purpura, an autoimmune disease. Due to the immune destruction of platelets, the number of platelets in peripheral blood decreases, and the not fully matured and larger platelets in bone marrow are released early, and an increased number of large platelets occurs. When hormone therapy is applied and the disease is controlled, the number of large platelets in the peripheral blood gradually decreases. In addition, some patients with acute myeloid acute leukemia may also have a high number of large platelets.