High platelet width may be caused by megaloblastic anemia, myelodysplastic syndrome and other diseases. 1. Megaloblastic anemia: It is due to the lack of folic acid and vitamin B12 in blood cells, which leads to DNA synthesis disorder and platelet dysplasia, resulting in the increase of giant platelets and the formation of platelets of different sizes, which contain a large number of platelets of larger size, and ultimately leading to high platelet width. 2. Myelodysplastic syndromes: a heterogeneous group of myeloid clonal disorders of hematopoietic stem cells. Hematopoietic dysfunction caused by abnormal proliferation and differentiation of hematopoietic stem cells may result in giant platelets, leading to high platelet width. In addition, acute myeloid leukemia, chronic granulocytic leukemia and other conditions can also occur, so patients with high platelet width should go to the hospital as soon as possible and receive standardized treatment under the guidance of the doctor.