Aplastic anemia: currently defined as a disease manifested mainly by immune-mediated hypoplasia of bone marrow and multilineage cytopenia of peripheral blood, without abnormal bone marrow and extramedullary infiltration and without bone marrow fibrous tissue hyperplasia. 1. Diagnostic criteria 1) At least two lineages of cytopenia (hemoglobin less than 10g/L, platelet count less than 50*109/L, neutrophil count less than 1.5*109/L), reticulocyte reduction and relative increase in lymphocytes; Fu Bin, Department of Hematology, Xiangya Hospital, Central South University 2) At least one part of bone marrow is hypoplasic or severely hypoplasic (if proliferation is active, there must be significant megakaryocyte 3) Except for other diseases causing allohemocytopenia, such as paroxysmal sleep hemoglobinuria, myelodysplastic syndrome, autoantibody-mediated allohemocytopenia, acute hematopoietic arrest, myelofibrosis, acute leukemia, malignant histiocytosis, etc. 4) Precautions: Detailed history of medication needs to be asked. A history of suspected disease requires avoidance of re-use of the drug. A history of specific infections before the onset of the disease and a history of teratogenic hepatitis need to be noted. Bone marrow biopsy specimens are generally easy to obtain, otherwise consider other diagnoses; trilineage is reduced in the bone marrow and may show pathological hematopoiesis in the red lineage but not in the granulocytic and megakaryocytic lineages; macrophage phagocytosis may be seen in early stage patients; bone marrow biopsy should obtain at least 2 cm of bone marrow and fully analyze the hematopoietic cellular composition as there may be active sites of hematopoiesis and puncture may show normal hyperplasia; early cells in the bone marrow should be reduced and if increased suggest possible hypoproliferative MDS or progression to myeloid leukemia; peripheral blood mononuclear cells are generally reduced, but if lacking, one needs to be alert for hairy cell leukemia. 5) Differential diagnosis: ① hypoproliferative MDS or AML: granulocytic and megakaryocytic pathological hematopoiesis, increased primitive cells, and increased reticulocyte scleroplasmin in residual hematopoietic tissue are not seen in AA; abnormal localization of precursor cells (ALIP) can help in the diagnosis of MDS but is not absolute; erythroid pathological hematopoiesis can be very common in AA. (ii) Childhood hypoproliferative ALL: 1-2% of children with ALL may have a period of bone marrow failure 3-9 months prior to typical ALL presentation, and leukopenia is more pronounced than thrombocytopenia; immunophenotyping may help in the diagnosis. (iii) Hairy cell leukemia: a small proportion of patients with this disease do not have splenomegaly but show complete blood cytopenia, bone marrow is often dry, bone marrow biopsy has hairy cell infiltration and increased reticulin; immunophenotyping CD20+,CD11c+,CD25+,FMC7+,CD103+,CD5-,CD10- and CD23-. ④Other such as: ITP, lymphoma and myelofibrosis, etc. 2. Typing criteria 1) Heavy aplastic anemia: bone marrow hematopoietic cell component less than 25%, or 25%-50%, of which the residual hematopoietic cells are less than 30%; blood picture meets any two of the following: neutrophils less than 0.5*109/L, platelets less than 20*109/L, reticulocyte count less than 20*109/L. 2) Very heavy aplastic anemia: meets the conditions of heavy aplastic conditions, neutrophil count is less than 0.2*109/L 3) Light: does not meet the criteria of heavy reoccurrence. Since the mortality rate of this disease is extremely high, it is necessary to make a clear diagnosis as soon as possible and start treatment immediately, and the timing of pre-treatment is extremely critical. Glucocorticoids should be avoided as much as possible during treatment, except for the prevention of allergy and prevention of serum sickness during ATG use. The treatment process not only needs to target the etiology, but also the related treatment such as infection control and blood transfusion support are life-saving treatments that should not be neglected, especially the follow-up treatment after immunosuppression which is most easily neglected and is extremely critical, and often problems occur at this stage leading to the abandonment of previous work.