Blood can be drawn during menstruation. The amount of blood that normal women bleed after each menstrual period fluctuates between 20-50ml, which is the amount of blood that the human body can afford, and the amount of blood drawn for each laboratory test is also the amount of blood that the patient’s body can tolerate. The human body’s hematopoietic function is always working, and the lost blood can be replenished through bone marrow hematopoiesis. Therefore, blood sampling during menstruation will not cause any problems due to blood loss, and women do not need to worry too much. If the patient’s menstrual flow is heavy and has developed severe anemia, it is recommended that the patient not undergo unnecessary blood tests to avoid further loss of blood, and consult the local hospital in time, and be hospitalized for blood transfusion treatment if necessary, so as to prevent the patient from experiencing hemorrhagic shock and endangering his/her life.