what are signs that you need a blood transfusion
1 Platelets and plasma may be used during surgery because they help your body stop bleeding.  You may get a transfusion of red blood cells for chronic anemia (lack of red blood cells). You may get platelets or plasma to treat a condition that affects blood clotting, such as hemophilia. You may need platelets if you had chemotherapy to treat cancer.
Treatment: Procedures. If you have severe anemia, you may need a transfusion of blood that matches your type. When the body's production of red blood cells doesn't work right, anemia caused by serious illnesses such as cancers and aplastic anemia may be treated or cured with a transplant.