A blood transfusion involves taking blood from one person (the donor) and giving it to someone else.

You may need a blood transfusion for a number of reasons, including:

  • to replace blood lost during major surgery, childbirth or a severe accident
  • to treat anaemia that has failed to respond to other treatments; anaemia is a condition where a person has low levels of red blood cells
  • to treat inherited blood disorders, such as thalassaemia or sickle cell anaemia

You can refuse a blood transfusion, but you need to fully understand the consequences of this before doing so. Some medical treatments or operations can't be safely carried out without a blood transfusion being given.

Read more about why a blood transfusion might be necessary.

The procedure

Blood is usually given through a plastic tube inserted into a vein in your arm. Each unit can take between 30 minutes and four hours. Depending on how much blood is needed, the whole procedure can take a significant length of time.

Read more about how a blood transfusion is performed.

How quickly is blood given?

  • A unit (bag) of red blood cells usually takes two to three hours to give. If needed, a unit can be given more rapidly – for example, to treat severe bleeding.
  • A unit of platelets or plasma is given in 30 to 60 minutes.


Blood donors are unpaid volunteers. They're carefully selected and tested to make sure the blood they donate is as safe as possible.

In the UK and other Western countries, there are strict regulations regarding blood donations and blood transfusions. The aim is to reduce the risk of a person being given blood contaminated with a virus, such as hepatitis C, or receiving blood from a blood group that's unsuitable for them.

Before making a blood donation, the potential donor is asked about their health, lifestyle and history.

Read more information about who can donate blood.

After blood has been donated, it's always tested for the following infections:

Compared to other everyday risks, the chances of getting an infection from a blood transfusion is very low.

You must be correctly identified to make sure you get the right blood transfusion. Wearing an identification band with your correct details is essential. You will be asked to state your full name and date of birth, and the details on your identification band will be checked before each bag of blood is given. You will be monitored closely during your transfusion.

Read more about the risks associated with blood transfusion.

What does blood do?

When a donor has given blood, special equipment is used to separate the donation into different blood components, including:

  • red blood cells – these transport oxygen around the body and are used to treat anaemia
  • platelets – these help to stop the bleeding when a person is cut or injured; platelet transfusions can be used to prevent excessive bleeding in certain groups of people with low platelet counts, such as those having chemotherapy treatment (powerful medication to treat cancers)
  • plasma – a liquid that makes up most of the volume of blood; plasma contains many nutrients needed by the body’s cells, as well as proteins that help the blood to clot if a patient is bleeding
  • white blood cells – these are used to fight infection

Page last reviewed: 07/01/2015

Next review due: 07/01/2017