Hemoglobin is hemoglobin, hemoglobin is the main component of red blood cells, it is an important index for evaluating anemia, and it decreases quickly most commonly due to pathological factors, such as acute blood loss, aplastic anemia and so on. 1. Excessive blood loss: hemoglobin decreases most commonly in acute blood loss such as peptic ulcer bleeding, ectopic pregnancy, placenta praevia and other triggered bleeding, trauma causing massive bleeding, disseminated intravascular coagulation disorders, hemorrhagic shock and so on. 2. Reduced production: aplastic anemia caused by bone marrow failure, iron deficiency anemia and megaloblastic anemia caused by lack of hematopoietic substances. 3. Excessive destruction: hemolytic anemia caused by excessive destruction of red blood cells. Reduced hemoglobin should go to the hematology department of the hospital in time to avoid delaying the condition.