source: University of Michigan

During a blood transfusion, a person (the recipient) receives healthy blood from another person (the donor). The donated blood is carefully screened for diseases before it is used. Before receiving a blood transfusion, the recipient’s blood is analyzed closely (using blood type) to make sure the donor blood is a close match to the recipient’s.

Blood is transfused into an arm vein slowly over 1 to 4 hours (except in an emergency when blood is transfused more quickly).

Blood transfusions can:
-Treat a sudden or short-term condition related to sickle cell disease.
-Treat severe complications of sickle cell disease.
-Prevent complications of sickle cell disease.
-Lower the risk of stroke in infants and children.
-Blood transfusions aren’t usually used to treat uncomplicated painful events or mild to moderate anemia.