To determine the cause of anemia, the following tests should be done: 1. Routine blood count, based on the red blood cell parameters in the routine blood count, including average red blood cell volume, average red blood cell hemoglobin volume, and average red blood cell hemoglobin concentration, can classify the anemia into red blood cell morphology, and can initially determine whether the anemia is macrocytic, orthocytic, or microcytic. In addition, reticulocyte count should be checked, which can indirectly reflect the proliferation and compensation of the red lineage in the bone marrow.2. Bone marrow examination, bone marrow cell smear can reflect the degree of proliferation of bone marrow cells, the proportion of each series of cells and morphological changes.3. Bone marrow biopsy can reflect the degree of proliferation of bone marrow hematopoietic tissue and cellular composition.4. If iron deficiency anemia is considered, serum iron, ferritin, transferrin and total iron binding capacity can be tested. If megaloblastic anemia is considered, folic acid and vitamin B12 levels can be checked. If hemolytic anemia is suspected, serum bilirubin, acid hemolysis test, Coombs test, CD55 and CD59 levels, urine ferritin test, and chromosomal genetic test should be done if necessary.