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Blood transfusion: why and how it is done

Guide Published

A blood transfusion gives red blood cells, plasma or platelets from a donor to someone who has lost blood or has a condition affecting their blood. The NHS describes it as generally safe, though complications can rarely occur.

Key points

  • Transfusions are used after major blood loss and for conditions that affect the blood or bone marrow.
  • Blood is matched to the person's blood group first, because the wrong ABO group can be life-threatening.
  • The NHS describes transfusion as generally safe, with complications such as infection or an allergic reaction rare.
  • All blood donated in the UK is tested for infection by NHS Blood and Transplant.

Why would someone need a blood transfusion?

The NHS says a transfusion can help when a person has lost a lot of blood, or has a condition that affects the blood or bone marrow. Platelets or plasma may be given to treat or prevent bleeding.

In children, transfusions may replace blood lost during an operation or after an accident, or treat conditions such as severe anaemia, sickle cell disease or thalassaemia. Blood components such as platelets and plasma, which help blood to clot, can also be given.

How is blood matched?

A blood sample is taken before the transfusion to check that donor blood is the right blood group.

Giving blood from the wrong ABO group can be life-threatening, which is why the checks are strict. The Rh D group also matters: Rh D negative women who could become pregnant are normally given Rh D negative red cells, to avoid harmful antibodies.

What happens during a transfusion?

Blood transfusions take place in hospital. Blood or a blood component is usually given through a thin tube into a vein.

The hospital team can explain what to expect on the day.

What are the risks and side effects?

The NHS describes a blood transfusion as generally safe. Rarely, complications such as an infection or an allergic reaction can happen, and they can appear a few hours, days or even weeks later.

Some people have mild side effects, such as a raised temperature or a skin rash. Pulse, temperature and blood pressure are monitored during the transfusion. Anyone who feels unwell after going home can contact the hospital team, NHS 111 or a GP, and 999 is for emergencies.

How safe is the blood supply?

All blood donated in the UK is tested for infection by NHS Blood and Transplant. Any donation that reacts in the initial tests is not used.

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Educational content. This article summarises public guidance and announcements in plain English for education. It is not medical advice and it cannot say what is right for you: speak to a clinician about your own health, call NHS 111 if you are unsure what to do and 999 in an emergency.