A high platelet distribution width is usually of no particular significance in clinical practice and does not indicate an abnormality in the patient’s body. A very significant increase in platelet distribution width may indicate a decrease in the number of platelets in the body. Platelet distribution width, or mean platelet volume distribution width, is an indicator of the degree to which platelet volume is dispersed in the peripheral blood, i.e., an indicator of how uniform the platelet volume is in the peripheral blood. An increase in platelet distribution width indicates that platelets in the peripheral blood are not uniform in size and have size differences. The most common cause is the presence of a large number of platelets in the peripheral blood, as in patients with autoimmune thrombocytopenia. Since peripheral platelets are severely damaged but have a high compensatory capacity, large underdeveloped platelets are released early, resulting in a wider distribution of peripheral platelets. In addition, after chemotherapy, with the gradual disappearance of myelosuppression, the width of platelet volume distribution in the peripheral blood increases, which is a signal of myelodysplasia.