What is a Blood Transfusion?

By Dr. Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

Blood transfusion refers to the administration of donated blood products such as red blood cells, platelets or plasma. Blood transfusion is indicated in the treatment of various conditions including trauma, bleeding disorders and blood loss due to surgery. Blood transfusion is required when blood loss has occurred or the body fails to produce enough blood or blood components to meet the body’s needs.

Blood transfusion essentially involves replacement of the blood components that are lacking. These include:

• Red blood cells (RBCs) containing the hemoglobin that carries oxygen to the various organs and tissues in the body. Patients with low hemoglobin (anemia) require blood transfusions to replace these RBCs. A blood transfusion is generally needed if the haemoglobin is below 70 g/L (grams per litre) but may also be necessary if the haemoglobin is between 70 g/L and 100 g/L. The procedure is not usually required when a person’s hemoglobin is above 100 g/L.
• Platelets are small cells in blood that aid blood clotting and help to prevent bleeding after injury. If a patient’s platelet count is low or the platelets do not function properly, a platelet transfusion may be required.

Blood donation

Blood is usually collected from voluntary blood donors. Donated blood undergoes extensive checking and testing to prevent the transmission of blood-borne infections through the transfusion of contaminated blood. Common infections that may be transmitted in this manner include HIV and Hepatitis B and C.

Risks associated with blood transfusion

Blood transfusion is associated with several risks. In the past, the transmission of infections was one of the most important risk factors associated with blood transfusion. Nowadays, this risk is much smaller due to stringent blood screening processes. Other risk factors associated with blood transfusion include:

• An allergic reaction to the blood may occur. These reactions range in severity from a mild skin reaction or fever, for example, through to more severe and life threatening reactions
• A severe allergic reaction may occur as a result of mismatched transfusion due to ABO or Rh incompatibility, for example. Blood is typed into 4 major groups: A, B, O and AB. In cases of ABO incompatibility, the reaction is invariably severe and leads to destruction of circulating donor RBCs, respiratory collapse and acute renal failure.
• Transfusion associated circulatory overload (TACO)
• Transfusion associated lung injury (TRALI)
• Over time, repeated blood transfusions may cause iron overload that leads to iron deposition in the tissues and organ injury.

Further Reading

• All Blood Transfusion Content
• History of Blood Transfusion
• Blood Transfusion Precautions
• Blood Transfusion Substitutes