Immature Reticulocyte Index (IRI) is a measure of the hematopoietic status of the red blood cells in the bone marrow. A low immature reticulocyte index indicates low hematopoiesis of red blood cells in the bone marrow. Common diseases include aplastic anemia and pure red blood cell aplastic anemia. Due to the damage of T-lymphocytes to human hematopoietic stem cells, resulting in hematopoietic stem cells can not be normal proliferation and division, there will be a reduction of the three lineages in the peripheral blood, which will also appear in the low reticulocyte index. In addition, patients with malignant tumors, especially leukemia patients, after high-dose chemotherapy, due to the damage of chemotherapeutic drugs to hematopoietic stem cells, hematopoietic function is low, and there will also be immature reticulocyte index is significantly low. However, as bone marrow suppression subsides and the number of red blood cells in the peripheral blood rises, the lowered immature reticulocyte index will gradually return to normal.