Anemia is a syndrome in which the volume of red blood cells in the peripheral blood of the human body decreases and falls below the lower limit of the normal range, resulting in insufficient oxygen supply to tissues and organs. 1. Clinically, the test of hemoglobin concentration is usually used instead of the test of red blood cell volume, and men with hemoglobin <120g/L and women <110g/L are considered to be anemic. 2. Different types of anemia are caused by different reasons. Clinically, there are common types of anemia caused by abnormal hematopoietic stem cells (e.g. aplastic anemia), anemia caused by insufficient hematopoietic raw materials (e.g. iron-deficiency anemia, megaloblastic anemia), and hemolytic anemia (e.g. thalassemia, sickle cell anemia), etc. In addition, gastrointestinal bleeding, menstruation, and other diseases may cause anemia. In addition, anemia may also occur in patients with gastrointestinal bleeding and women with excessive menstrual flow. 3. Common clinical manifestations of anemia include dizziness, headache, tinnitus, insomnia, excessive dreaming, memory loss, palpitation, shortness of breath, dyspnea, loss of appetite, abdominal distension, nausea, constipation, and pallor of skin and mucous membranes. Warm reminder: patients who are found to be anemic in routine blood tests should consult the hematology department in time to further improve the relevant examinations, clarify the cause of the disease, and if necessary, be treated under the guidance of a doctor.