Blood transfusion is the process of transferring blood or blood-based products from one person into the circulatory system of another. Blood transfusions can be life-saving in some situations, such as massive blood loss due to trauma, or can be used to replace blood lost during surgery.
Blood transfusions may also be used to treat a severe anaemia or thrombocytopenia caused by a blood disease. People suffering from hemophilia or sickle-cell disease may require frequent blood transfusions. Early transfusions used whole blood, but modern medical practice commonly uses only components of the blood.
Blood transfusions can be grouped into two main types depending on their source:
- ''Homologous transfusions'', or transfusions using the stored blood of others. These are often called ''Allogeneic'' instead of homologous.
- ''Autologous transfusions'', or transfusions using the patient's own stored blood.
Donor units of blood must be kept refrigerated to prevent bacterial growth and to slow cellular metabolism. The transfusion must begin within 30 minutes after the unit has been taken out of controlled storage.
Blood can only be administered intravenously. It therefore requires the insertion of a cannula of suitable caliber.
Before the blood is administered, the personal details of the patient are matched with the blood to be transfused, to minimize risk of transfusion reactions. Clerical error is a significant source of transfusion reactions and attempts have been made to build redundancy into the matching process that takes place at the bedside.
A unit (up to 500 ml) is typically administered over 4 hours. In patients at risk of congestive heart failure, many doctors administer a diuretic to prevent fluid overload, a condition called Transfusion Associated Circulatory Overload or TACO. Acetaminophen and/or an antihistamine such as diphenhydramine are sometimes given before the transfusion to prevent other types of transfusion reactions.
Blood is most commonly donated as whole blood by inserting a catheter into a vein and collecting it in a plastic bag (mixed with anticoagulant) via gravity. Collected blood is then separated into components to make the best use of it. Aside from red blood cells, plasma, and platelets, the resulting blood component products also include albumin protein, clotting factor concentrates, cryoprecipitate, fibrinogen concentrate, and immunoglobulins (antibodies). Red cells, plasma and platelets can also be donated individually via a more complex process called apheresis.
In developed countries, donations are usually anonymous to the recipient, but products in a blood bank are always individually traceable through the whole cycle of donation, testing, separation into components, storage, and administration to the recipient. This enables management and investigation of any suspected transfusion related disease transmission or transfusion reaction. In developing countries the donor is sometimes specifically recruited by or for the recipient, typically a family member, and the donation immediately before the transfusion.
Risks to the recipient
There are risks associated with receiving a blood transfusion, and these must be balanced against the benefit which is expected. The most common adverse reaction to a blood transfusion is a ''febrile non-hemolytic transfusion reaction'', which consists of a fever which resolves on its own and causes no lasting problems or side effects.
Hemolytic reactions include chills, headache, backache, dyspnea, cyanosis, chest pain, tachycardia and hypotension.
Blood products can rarely be contaminated with bacteria; the risk of severe bacterial infection and sepsis is estimated, as of 2002, at about 1 in 50,000 platelet transfusions, and 1 in 500,000 red blood cell transfusions.
There is a risk that a given blood transfusion will transmit a viral infection to its recipient. As of 2006, the risk of acquiring hepatitis B via blood transfusion in the United States is about 1 in 250,000 units transfused, and the risk of acquiring HIV or hepatitis C in the U.S. via a blood transfusion is estimated at 1 per 2 million units transfused. These risks were much higher in the past before the advent of second and third generation tests for transfusion transmitted diseases. The implementation of Nucleic Acid Testing or "NAT" in the early 00's has further reduced risks, and confirmed viral infections by blood transfusion are extremely rare in the developed world.
Transfusion-associated acute lung injury (TRALI) is an increasingly recognized adverse event associated with blood transfusion. TRALI is a syndrome of acute respiratory distress, often associated with fever, non-cardiogenic pulmonary edema, and hypotension, which may occur as often as 1 in 2000 transfusions. Symptoms can range from mild to life-threatening, but most patients recover fully within 96 hours, and the mortality rate from this condition is less than 10%.. Although the cause of TRALI is not clear, it has been consistently associated with anti HLA antibodies. Because anti HLA strongly correlate with pregnancy, several transfusion organisations (Blood and Tissues Bank of Cantabria, Spain, National Health Service in Britain) have decided to use only plasma from men for transfusion.
Other risks associated with receiving a blood transfusion include volume overload, iron overload (with multiple red blood cell transfusions), transfusion-associated graft-vs.-host disease, anaphylactic reactions (in people with IgA deficiency), and acute hemolytic reactions (most commonly due to the administration of mismatched blood types).
Transformation from one type to another
Scientists working at the University of Copenhagen reported in the journal Nature Biotechnology in April 2007 of discovering enzymes, which potentially enable blood from groups A, B and AB to be converted into group O. These enzymes do not affect the Rh group of the blood.
Objections to blood transfusion
Objections to blood transfusions may arise for personal, medical, or religious reasons. For example, Jehovah's Witnesses object to blood transfusion primarily on religious grounds - they believe that blood is sacred; although they have also highlighted possible complications associated with transfusion.
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