There are several reasons for low serum iron: First, it may be due to insufficient iron intake, if infants, adolescents, pregnant and lactating women, their iron needs are high, if not supplemented with sufficient eggs, meat and other foods with high iron content, it is easy to cause iron deficiency. Second, if some friends suffer from duodenal ulcer or unexplained diarrhea, chronic enteritis, can also lead to iron absorption disorders, resulting in low iron in the serum phenomenon. Third, if there is a hiatal hernia, esophageal or gastric varices, gastroduodenal ulcer, gastrointestinal polyps, pulmonary hemorrhage, tuberculosis or heavy menstrual flow, it can lead to excessive iron loss, resulting in low serum iron.