Packed red blood cell transfusions are given to increase the oxygen-carrying capacity of the patient’s blood. There may be several reasons why your blood supply is low. You may have a low hemoglobin and hematocrit reading (anemia), loss of blood during surgery or trauma, or bleeding internally in the intestines. The loss of blood may be sudden (acute) or slow (chronic). A packed red blood cell transfusion is almost always necessary for a blood loss of more than 30 percent. Transfusions are indicated when the blood pressure decreases and the heart rate increases during an episode of bleeding. Chronic anemia patients may not need a blood transfusion if they are not showing symptoms of a crisis. Chronic anemia should be treated with methods other than transfusions.