Anemia is a common symptom or syndrome in the pediatric period and refers to a lower than normal number of red blood cells per unit volume, hemoglobin volume, and red blood cell pressure product in the terminal blood, or one of them is significantly lower than normal. Due to geographical factors, the normal values of these three items vary both domestically and internationally. Because the erythrocyte count and hemoglobin volume are not necessarily parallel to the erythropoietic pressure, the erythrocyte count and hemoglobin volume are often used as clinical criteria to measure the presence or absence of anemia. It should be noted that the red blood cell count and hemoglobin volume are related to blood volume. For example, when the blood volume is reduced (dehydration), although the red blood cell count and hemoglobin volume per unit volume are normal, there may be anemia. In this case, the red blood cell count and hemoglobin volume alone do not reflect the real situation of anemia. Pathogenesis Nutritional iron deficiency anemia is the most common type of pediatric anemia, with the highest incidence in infants and children. The main clinical feature is small cell hypochromic anemia, so it is also known as nutritional small cell anemia. The common anemia in children is iron deficiency anemia. This is due to: (l) Insufficient congenital iron stores in children The iron obtained by normal full-term newborns from their mothers is sufficient for their hematopoietic needs for 3 to 4 months after birth. However, prematurity, twin births, fetal blood loss and maternal iron deficiency anemia can make the pediatric iron stores insufficient. The iron obtained from the mother during fetal life is most available in the last trimester of pregnancy. Normal full-term newborns have iron stores of about 25”0-300 mg (average 60-70 mg/kg). The stored iron and the iron released by the destruction of red blood cells after birth are sufficient for hematopoiesis within 3 to 4 months after birth. If iron stores are insufficient, iron deficiency anemia is likely to occur earlier in infancy. Severe iron deficiency anemia in the mother, low birth weight due to prematurity or twin births, and blood loss from the fetal circulation (e.g., fetal transfusion to the mother or transfusion to another sibling twin) are all causes of reduced iron stores in the newborn. Delaying the ligation of the umbilical cord after birth and squeezing the blood out of the cord by hand can result in 75 ml of extra blood or 35 mg of iron for the newborn. (2) Insufficient iron intake The diet of newborns is mainly human milk or cow’s milk, and the iron content of both human milk and cow’s milk is low, and simple feeding with milk without timely addition of supplementary food containing more iron is prone to anemia. Human milk and cow’s milk have low iron content (<0.21 mg/dL), which is not enough for infants, so if they are fed with milk alone without adding supplemental food containing more iron in time, they are prone to iron deficiency anemia. Although spinach contains more iron in food, it is poorly absorbed, while soybeans are higher in iron in plants and have a higher absorption rate, so they can be preferred. The absorption rate of iron in meat is higher, while the absorption rate of iron in eggs is lower in animal foods. Iron deficiency anemia can also be caused by long-term diarrhea, digestive tract malformation, intestinal malabsorption and other causes of iron absorption disorders. (3) Rapid growth and development Rapid growth and development during infancy: 2 times the weight at birth at 3 to 5 months, 3 times the weight at birth at 1 year, and even faster if the baby is born prematurely. Due to the increase in weight, the blood volume also increases rapidly, and iron deficiency can easily occur at this time, causing anemia. (4) Excessive loss of iron Normal infants excrete more milling per day than adults, and lose relatively more iron from the skin. In addition, some diseases such as chronic diarrhea, intussusception, intestine, polyps, etc. can increase iron consumption and cause anemia. Note: Pediatric anemia is not due to simply eating poorly In the era of material scarcity, children did not eat well and could not keep up with nutrition, which was the main cause of iron deficiency anemia. But nowadays, the variety of food is becoming more and more abundant, and families are getting better and better off, so children are given expensive food, but iron deficiency anemia still occurs from time to time, which is a problem with the food structure. The iron stored in the body of a full-term child who is breastfed is generally sufficient for half a year of growth and development, after which iron needs to be taken in through complementary foods. And iron-rich foods include lean meat, pork liver, mushrooms, fungus, etc. Only by eating more of these foods can we ensure the intake of iron. However, many children wait until ten months or one year before they start adding complementary foods, missing the best time to learn to chew (eight to nine months), and it is quite difficult to correct bad eating habits. Children who are always reluctant to eat dishes, iron supplementation can not keep up, anemia is very easy to occur. "Not to mention that many children also have the habit of partial eating, coupled with the misconception that Cantonese people just drink soup without crumbs, can affect the intake of iron." Premature birth and disease can also cause iron deficiency anemia in children. The former is because the fetal iron stores are mainly concentrated in the late 3-4 months of pregnancy, too early birth will make the body low iron stores, while the latter is either because too much iron is lost, or disease affects the gastrointestinal function thus reducing iron absorption.