Platelet distribution width is an indicator of the dispersion of platelet volume in peripheral blood, which is often expressed clinically by the coefficient of variation of platelet volume in peripheral blood, with a normal range of 9%-17%, below 9% indicating low platelet distribution width and above 17% indicating high platelet distribution width. Low platelet distribution width is common when the hematopoietic function is reduced, such as patients with aplastic anemia or patients with malignant tumor after radiotherapy or chemotherapy, the bone marrow enters the myelosuppression phase and the hematopoietic function is reduced, then the platelet distribution width will be low. High platelet distribution width is common in cases of excessive platelet destruction in peripheral blood but good bone marrow hematopoietic function, such as immune thrombocytopenia, some acute granulocytic leukemia, erythroleukemia, etc., which may also have high platelet distribution width.