Low serum iron means that the concentration of iron in the serum is lower than the normal range. The most common disease of low serum iron is iron deficiency anemia, and the common causes of iron deficiency anemia include insufficient iron intake, iron absorption disorders, and iron loss, etc. Insufficient iron intake is common in women of childbearing age and children during the growth period, because the demand for iron in these people is significantly higher than normal, and if iron-rich foods are not added to the diet in time, it is easy to cause insufficient iron intake. Impaired absorption of iron is common in patients with chronic gastrointestinal diseases, as the presence of digestive system disorders prevents normal absorption of iron and eventually causes low serum iron. Iron loss, commonly seen in various chronic blood loss conditions, such as chronic peptic ulcer bleeding, chronic nasal bleeding, chronic hemorrhoid bleeding, etc. As all the iron in the red blood cells is lost and cannot be reabsorbed and utilized, low serum iron can also occur.