Platelet distribution width is an indicator of the dispersion of platelet volume size in peripheral blood, that is, a parameter that reflects the uniformity of platelet size in peripheral blood. A low platelet distribution width indicates that the platelets in the peripheral blood are uniform in size and do not differ significantly. It can be seen in some normal individuals and also in bone marrow hematopoietic disorders, the most common being aplastic anemia. In aplastic anemia, a low platelet volume distribution width occurs due to damage to hematopoietic stem cells, bone marrow hematopoietic failure, and decreased ability of megakaryocytes to produce platelets. After chemotherapy is given to leukemia patients, if severe bone marrow suppression occurs, low platelet distribution width may also occur. Therefore, if a low platelet distribution width occurs, it is important to first rule out the presence of aplastic anemia or other hematologic malignant diseases.