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.
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.
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.
After blood has been donated, it's always tested for the following infections:
HIV and AIDS
human T-cell lymphotropic virus (HTLV) – a rare but potentially serious virus, which in some people can cause a type of leukaemia that's usually fatal
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.
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
Why a blood transfusion is necessary
There are several different types of blood transfusion. Whether you need one depends on a number of factors.
your medical history
the type of operation you're having
the seriousness of your condition
An average-sized adult has about five litres of blood in total. Small amounts of blood loss (up to 1.5 litres) can be replaced with a salt solution, which your body replaces with new red blood cells over the following weeks.
The different types of blood transfusions are described below.
Red blood cell transfusions
The main reason for a red blood cell transfusion is to treat anaemia. Anaemia occurs when the body doesn't have enough red, oxygen-carrying blood cells, which means the body’s tissues and cells aren't getting enough oxygen.
Anaemia can develop as a result of severe blood loss – for example, as a complication during childbirth or as a result of injury or surgery. Anaemia can also be caused by:
health conditions in which red blood cells are produced at a reduced rate – for example, in anaemia due to lack of iron, vitamin B12 or folate (usually treated without the need for blood transfusion), and some types of cancers, such as acute myeloid leukaemia and lymphoma
health conditions that disrupt the normal production of red blood cells – such as sickle cell anaemia and thalassaemia
conditions or factors that lead to red blood cells being destroyed – for example, in some types of infections such as malaria, the use of certain medicines, toxins such as alcohol or lead poisoning, or as a result of the immune system mistakenly attacking healthy red blood cells
If you're told that you might need a blood transfusion, you should ask why it's necessary and whether there are alternative treatments. You have the right to refuse a blood transfusion, but you need to fully understand the outcome of this before doing so. Some medical treatments or operations can't be safely carried out without a blood transfusion.
A platelet transfusion is used to treat people who have very low levels of platelet cells in their blood. This is known as thrombocytopenia.
If you have thrombocytopenia, you're at risk of excessive bleeding, either through a minor accident, cut or graze, or as a result of surgery or dental work.
Causes of thrombocytopenia that may require treatment with a platelet transfusion include:
cancers – such as leukaemia or lymphoma
chemotherapy or bone marrow transplantation – which reduces the production of platelets
chronic liver disease or cirrhosis (scarring of the liver, which has many causes, including alcohol abuse)
sepsis or severe infection – this can cause abnormal clotting and low platelets
Plasma is the fluid in the blood containing proteins that help the blood to clot. A transfusion of plasma may be needed if there's severe bleeding, such as after surgery, trauma or childbirth. A transfusion may also be needed in conditions (such as liver disease) that affect the production of clotting proteins.
Granulocytes are a type of white blood cell that help to fight infection. Granulocyte transfusions aren't commonly used, but may be needed if there's a severe infection that's not responding to antibiotics after chemotherapy or bone marrow transplantation.
Surgeons always try to carry out surgery to minimise the amount of blood lost. In recent years, this has become easier, due to the increasing use of keyhole surgery (laparoscopic surgery), where only small cuts are made in the body.
However, some types of surgical operations and procedures have a higher risk of blood loss; therefore, a blood transfusion is more likely to be needed.
It may be possible to use a procedure called intra-operative cell salvage. It collects your blood that's lost during the surgery, and it can be returned back to you. Ask your doctor or nurse if intra-operative cell salvage is appropriate for the type of surgery you’re having.
It's no longer possible to routinely collect your own blood in advance of your surgery.
Preparing for a blood transfusion
If you're going to receive a blood transfusion as part of a planned course of treatment, the doctor, nurse or midwife planning your transfusion will usually obtain your informed consent for the procedure.
In obtaining consent, they should:
explain why a blood transfusion is required and if there are any alternatives
explain potential risks or complications associated with the transfusion
There may be circumstances when it's not possible to obtain consent before a transfusion – for example, if someone is unconscious after a major accident.
How blood is given
A sample of your blood will be taken before the transfusion to check that the blood you receive is compatible with your own blood.
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.
Blood is usually given through a tiny plastic tube called a cannula, which is inserted into a vein in your arm. The cannula is connected to a drip and the blood runs through the drip into your arm.
Depending on the underlying condition and the type of other treatment needed, some patients may have a larger tube, which is known as a central line, inserted into a vein in their chest.
Alternatively, a peripherally inserted central catheter (PICC line) may be inserted in the crook of the arm.
During the transfusion
There may be some discomfort when the tube is put into the vein, but you shouldn't feel anything during the transfusion.
You'll be observed at regular intervals, but if you start to feel unwell during or shortly after your transfusion, you should tell a member of staff immediately.
Some people may develop a temperature, chills or a rash. These reactions are usually mild and easily treated with paracetamol or by slowing down the blood transfusion.
Severe reactions to blood are rare. If they occur, staff are trained to recognise and treat them. If you have any concerns, discuss them with your doctor, nurse or midwife.
A single unit of blood can take between 30 minutes and four hours to be given.
Risks of a blood transfusion
Blood transfusions are a fairly common procedure. The risk of serious side effects is low, as your blood is tested against the donor blood to make sure it is compatible, and you will be monitored regularly during the transfusion.
Having an allergic reaction to the donated blood is a rare complication of a blood transfusion. In 2013, there were 320 reported cases of allergic reactions after a blood transfusion in the UK.
An allergic reaction is caused by the body’s immune system reacting to proteins or other substances in the donated blood. The symptoms of the reaction are usually mild and occur during or shortly after the transfusion.
Common symptoms include:
a raised, red, itchy skin rash (urticaria)
swelling of the hands, arms, feet, ankles and legs (oedema)
Less common symptoms include:
high temperature (fever) of or above 38C (100.4F)
shortness of breath
swelling of the lips or eyelids
These types of reactions can usually be successfully managed by slowing down or stopping the transfusion and treating the symptoms with antihistamines and, in some cases, paracetamol.
Anaphylaxis is a more serious and potentially life-threatening allergic reaction to antibodies or other substances in the blood. In 2013, there were 33 cases of anaphylaxis associated with blood transfusions in the UK.
The symptoms of anaphylaxis may occur as soon as the blood transfusion begins. They include:
severe shortness of breath
feeling faint or clammy
a rash or swelling of lips or eyelids
Treatment for anaphylaxis is usually an injection of a type of medication called adrenaline.
Occasionally, too much blood is transfused into the body in too short a time for the body to properly cope with it. This is known as fluid overload. It’s more common in people who are elderly or frail, and in those who have a lower body weight.
The excess fluid can result in the heart being unable to pump enough blood around the body (heart failure). The lungs also become filled with fluid, which can result in shortness of breath. Older patients and those with serious health conditions, such as heart disease, are at greater risk of fluid overload.
There were 34 cases of fluid overload due to blood transfusion reported in the UK during 2013.
It is treated by giving a medicine to remove excess fluid from the body (diuretic), and by reducing the speed of the transfusion in the future.
A rare but very serious risk associated with blood transfusions is transfusion-related acute lung injury (TRALI). It occurs more often with platelets and plasma than with red cells.
TRALI is a poorly understood condition, in which a person’s lungs suddenly become very inflamed within six hours of the transfusion. The high levels of inflammation cause the lungs to become starved of oxygen. In some cases, this can be fatal.
Most experts believe that some type of abnormal immune response causes the inflammation associated with TRALI.
Treatment for TRALI requires using a ventilator to provide the body with oxygen until the inflammation of the lungs subsides.
A haemolytic transfusion reaction (HTR) is when the immune system reacts to the donated blood and begins attacking the blood cells.
HTRs can happen during or soon after transfusion, or they can be delayed, happening a few days or even a week after transfusion. Haemolytic reactions can cause symptoms like other transfusion reactions, but the urine may turn darker, due to destruction of red blood cells.
HTRs are rare. They may be caused by:
a rare antibody that couldn’t be picked up during the checking procedure
in delayed reactions, a new antibody can develop after transfusion, which can break down the blood that has been transfused
in very rare circumstances, the wrong blood being given to a patient; this is why great care is taken to make sure the details on the sample tube are correct, and why checks on the patient and the bag of blood are carried out before starting the transfusion
Bacterially contaminated blood
Despite every effort being made to keep donated blood germ-free (sterile), bacteria can occasionally develop in donated blood, but this is very rare. Donations of platelets are particularly vulnerable to contamination, because they need to be stored at room temperature.
If a person receives a donation of contaminated blood, they may develop symptoms of blood poisoning (sepsis), including:
a fast heartbeat
cold, clammy skin
changes in mental states, such as confusion
Sepsis usually needs to be treated with injections of antibiotics – see treating sepsis for more information.
There have been no cases of bacterial infections associated with contaminated blood in the UK since 2009.
Viral contaminated blood
It’s extremely rare for someone to develop a viral infection from a blood transfusion, as the blood services use strict testing processes. For example, it is estimated that:
the risk of getting hepatitis B is about 1 in 1.3 million
the risk of getting hepatitis C is about 1 in 28 million
the risk of getting HIV is about 1 in 6.5 million
There hasn't been a recorded case of someone developing a viral infection from a blood transfusion since 2005.
Variant Creutzfeldt-Jakob disease (vCJD)
Creutzfeldt-Jakob disease (CJD) is a rare and fatal condition that causes worsening brain damage over time.
A form of this condition called variant Creutzfeldt-Jakob disease (vCJD), which is usually caused by eating meat infected with bovine spongiform encephalopathy (BSE, or "mad cow disease"), can be passed on through a blood transfusion. However, this is extremely rare.
In the UK, about 2.1 million units of blood components are transfused each year, and to date there have only been four cases of vCJD linked to transfusions.
As a precautionary measure, to reduce the risk of transmitting vCJD, people who have received a blood transfusion since 1980 are not currently able to give blood.