Many people have anemia, and it is the most common reason for hematology clinic visits. I hope this will be of some help to you. The first thing is to distinguish the size of the red blood cell volume, that is, whether the textbook says small cell anemia, large cell anemia, or orthocytic anemia. The most common cause of small cell anemia is iron deficiency anemia, and the most common cause is caused by chronic blood loss. Then there are many causes of chronic blood loss, including excessive menstruation for female patients, gastrointestinal problems for male patients, and even bleeding hemorrhoids in some cases. For elderly iron deficiency anemia, malignant lesions of the gastrointestinal tract should be considered. In our department, a considerable number of elderly patients with iron deficiency anemia are finally diagnosed as gastrointestinal tumors, and some are lymphomas of the gastrointestinal tract. If the effect of oral iron is poor, intravenous iron supplementation can be used if malignant diseases are excluded, which is very effective. In Guangdong, small cell anemia may be thalassemia, but this is not common in our province. Large cell anemia is most commonly caused by a deficiency of folic acid and vitamin B12, which can be supplemented with a certain amount of folic acid and vitamin B12. However, for a small number of patients with myelodysplastic syndromes there are cases of megaloblastic anemia, which should be distinguished from ordinary macrocytic anemia. Lastly, the most complicated anemia is orthocytic anemia, in which the volume of red blood cells is not significantly abnormal to normal red blood cells. The decrease in white blood cells may be due to myelodysplastic syndrome or hypoproliferative disorders such as aplastic anemia, or immune-related diseases, as well as certain specific types of leukemia. If there are abnormally elevated white blood cells and decreased platelets, it may be a complex condition such as leukemia, lymphoma, multiple myeloma, or malignant bone marrow invasion. In conclusion, a simple routine blood test is very important for hematologists, and a lot of information can be read from it, which is very important for further examination and treatment.