Blood transfusion

A blood transfusion transfers whole blood or one or more blood components into a recipient’s circulation, usually through an intravenous line. It may be used to replace blood lost through injury or surgery, or to support people whose bodies do not make enough of a needed blood component. The clinical purpose depends on the patient's condition and which component is required; transfusion is a medical treatment chosen in context, not a single treatment for every kind of blood problem.

Donated blood can be transfused as whole blood, but it is often separated into components. Red blood cells carry oxygen, platelets help blood clot, and plasma is the liquid portion that contains clotting proteins and other substances. Blood services may also prepare components such as cryoprecipitate. Processing can allow one donation to meet different patients’ needs, rather than giving every recipient all parts of the donation.

Before a planned red-cell transfusion, laboratories generally determine the recipient’s ABO and RhD blood groups, screen for antibodies that could react with donor red cells, and check compatibility with the selected unit. A crossmatch is a final compatibility check. Correct patient identification and sample labelling are essential, and testing procedures can differ with the blood component and urgency of treatment.

Blood services also screen donations for infections and manage collection, processing and storage under quality systems. The World Health Organization recommends screening donated blood for HIV, hepatitis B, hepatitis C and syphilis, while noting that some countries cannot yet screen every donation for all of these infections. Screening and matching make transfusion much safer, but do not remove every risk: recipients can have immune or other adverse reactions, and no blood supply can be considered entirely risk-free.

Attempts to transfer blood were made centuries before the biological reasons for incompatible reactions were understood. In the early 1900s, physician Karl Landsteiner's experiments helped classify human blood into groups, providing a basis for selecting compatible blood; the AB group was identified soon afterward. Landsteiner received the 1930 Nobel Prize in Physiology or Medicine for his discovery of human blood groups. Later work identified the Rh blood-group system. Knowledge of blood groups transformed transfusion from a poorly predictable intervention into a procedure that could be matched more systematically.

A transfusion depends on more than the procedure at a bedside: blood must be donated, tested, processed, stored and distributed so that an appropriate component is available when needed. WHO recommends coordinated national blood systems and a stable base of voluntary, unpaid donors. Its reporting also shows that access to safe and timely blood varies substantially between countries. Blood services therefore combine clinical practice with public-health work, including quality oversight, infection screening, donor care and monitoring of adverse events. Appropriate use matters too: unnecessary transfusions can expose patients to avoidable risk and reduce supplies available to people who need them.