Transfusion is the process of transferring whole blood or blood components from one person (donor) to another (recipient), to restore lost blood, to improve clotting time, and to improve the ability of the blood to deliver oxygen to the body's tissues. Whole blood is used exactly as it was received from thedonor. Blood components are parts of whole blood, such as red blood cells (RBCs), plasma, platelets, clotting factors, immunoglobulins, and white blood cells. Use of blood components is a more efficient way to use the blood supply, because blood that has been processed (fractionated) into components can beused to treat more than one person.

Whole blood is generally used when a person has lost a lot of blood by injuryor surgical procedures and is given to help restore the blood volume, whichis essential for maintaining blood pressure. Red blood cells are the blood component most frequently used for transfusion. As only cells in the body thattransport oxygen, a transfusion of RBCs increases the amount of oxygen that can be carried to the tissues of the body. RBCs that have been separated fromthe liquid plasma (packed RBCs) are given to people who have anemia or who have lost a lot of blood. Platelets are another component frequently given by transfusion. Platelets are a key factor in blood clotting. The clear fluid that carries blood cells (plasma) also contains blood-clotting factors. The platelets and plasma clotting factors are extracted from donated blood and concentrated for use. These factors are used to treat people with clotting disorders, such as hemophilia.

For donors, the process of giving blood is very safe. Only sterile equipmentis used and there is no chance of catching an infection from the equipment. There is a slight chance of infection at the puncture site if the skin is notproperly washed before the collection needle is inserted. Some donors feel light-headed upon standing for the first time after donating. Occasionally, a donor will faint. Donors are advised to drink lots of liquids to replace the fluid lost with the donated blood. Strenuous exercise should be avoided for the rest of the day. Most patients have very slight symptoms or no symptoms atall after donating blood.

For recipients, a number of precautions must be taken. The blood given by transfusion must be matched with the recipient's blood type. Generally, patientsare limited to receiving only blood of the exact same ABO and Rh type as their own. For example, a person with B+ blood can only receive blood or blood cells from another person with B+ blood. An exception is blood type O, calledthe universal donor, because people of all blood types can accept it. Incompatible blood types can cause a serious adverse reaction (transfusion reaction). Blood is introduced slowly by gravity flow directly into the veins (intravenous infusion) so that medical personnel can observe the patient for signs ofadverse reactions. People who have received many transfusions can develop animmune response to some factors in foreign blood cells. Though many effortsare made to ensure a safe blood supply, infectious diseases can occasionallybe transmitted through donated blood.

Each year in the United States, about 14,000,000 pints of blood are donated.Blood collection is strictly regulated by the Food and Drug Administration (FDA). The FDA has rules for the collection, processing, storage, and transportation of blood and blood products. In addition, the American Red Cross, the American Association of Blood Banks, and most states have specific rules for the collection and processing of blood. The main purpose of regulation is to ensure the quality of blood and to prevent the transmission of infectious diseases through donated blood. Before blood and blood products are used, they are extensively tested for infectious agents, such as hepatitis and AIDS.

Autologous transfusion is a procedure in which patients donate blood for their own use. Patients who are to undergo surgical procedures for which a bloodtransfusion might be required may elect to donate a store of blood for the purpose ahead of time. Directed donors are family or friends of the patient whoneeds a transfusion. Blood that is not used for the identified patient becomes part of the general blood supply.

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