Anemia can be caused by the following reasons: 1 Decreased erythropoiesis includes two conditions: lack of hematopoietic substances and poor hematopoietic function. The former is iron deficiency anemia and nutritional megaloblastic anemia. , often due to the lack of raw materials necessary for erythropoiesis, such as iron, vitamin B 12, folic acid or protein, or malabsorption caused by chronic infectious diseases, or because some children grow too fast and need more, so the best way to avoid anemia is to have a balanced diet and not be picky eaters. Aplastic anemia is common in hematopoietic dysfunction. If normal hematopoietic tissue is occupied by abnormal substances such as lymphocytes and leukemia cells, it will also reduce hematopoietic function and cause anemia. 2. hemolytic anemia hemolysis can be caused by internal and external causes of red blood cells. The former, such as bean diseases caused by red cell membrane defects and thalassemia caused by abnormal hemoglobin; The latter, such as neonatal ABO hemolysis, infection, burns, poisoning and so on, can also destroy red blood cells and cause hemolysis. Hemolytic anemia has a common feature, that is, there are different degrees of yellow staining of the skin, and different degrees of splenomegaly can be found during physical examination. 3. Blood loss can be divided into acute and chronic blood loss. The former is hemorrhagic disease, hemophilia, idiopathic thrombocytopenic purpura or traumatic hemorrhage such as splenic rupture. Chronic blood loss is common in digestive tract ulcer, anal fissure, hookworm disease and so on. Although the amount of blood loss is not much each time, it will accumulate over time and the total amount is quite large, which will also cause anemia. So iron deficiency anemia is just a kind of anemia. References:

What is anemia? Anemia means that the total amount of red blood cells in systemic blood drops below normal. However, due to the complexity of the measurement technology of total red blood cells in systemic blood, it generally means that the concentration of hemoglobin in peripheral blood is lower than the normal standard of patients of the same age, gender and region. The domestic normal standard is slightly lower than that of foreign countries. In coastal and plain areas, if the hemoglobin of adult males is lower than 12.5g/dl and that of adult females is lower than 1 1.0g/dl, it can be considered as anemia. /kloc-the normal value of hemoglobin in children under 0/2 years old is about 15% lower than that in adult men, and there is no significant difference between boys and girls. Areas with high altitude are generally higher. The decrease of red blood cell count in anemia patients is generally proportional to the decrease of hemoglobin concentration, but the decrease of red blood cell count in small cell hypopigmentation anemia is relatively less than the decrease of hemoglobin, so the red blood cell count cannot be lower than normal when anemia is mild. On the contrary, in macrocytic anemia, the hemoglobin concentration is relatively high, while the red blood cell count is low. When the total blood volume has not returned to normal after dehydration, water retention or acute massive blood loss, the concentration of hemoglobin can not accurately reflect the true degree of anemia, so the influence of these factors on anemia should be considered in clinic. In addition, when acute massive intravascular hemolysis occurs, the plasma contains high concentration of free hemoglobin, and the hemoglobin determination result is higher than the actual anemia degree. In this special case, hematocrit and red blood cell count can better reflect the degree of anemia. Anemia can be divided into several types according to morphology. The morphological classification of anemia is mainly based on the two morphological characteristics of mean red blood cell volume (MCV) and mean red blood cell hemoglobin concentration (MCHC), and all anemia can be divided into three types: normal cell type, low pigment small cell type and large cell type. (1) normal cell anemia: MCV is in the normal range, that is, 80 ~ 100 fl, and MCHC is mostly in the normal range, that is, 32% ~ 36%, and a few are slightly lower than the normal value. If reticulocyte count is high, MCV may exceed the normal range. There are acute hemorrhagic anemia, aplastic anemia, secondary anemia caused by chronic infection, inflammation, renal failure, liver disease, endocrine disorders, malignant tumors and most hemolytic anemia. (2) Small cell hypochromic anemia: MCV 100 fl, MCHC > 36%. There are megaloblastic anemia caused by folic acid or vitamin B 12 deficiency, and megaloblastic anemia caused by other reasons or metabolic disorders. The advantage of this classification is that it can be inferred from the morphological characteristics of red blood cells.