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Blood transfusion

A transfusion is when blood, or one of the different parts of blood, is given into your bloodstream through a small tube (cannula) put into a vein, usually in your arm. A blood transfusion can be lifesaving and may be used to replace blood that has been lost, for example during an operation or in an accident, or to treat anaemia.

Your blood is made up of many different components including:

  • red blood cells – these contain haemoglobin, which carries oxygen around your body
  • white blood cells – these are part of your immune system and are important for fighting infection
  • platelets – these help your blood to clot
  • plasma – this is the fluid that carries cells around your body

You can have a transfusion of red blood cells (this is what is usually called a blood transfusion) or you can have a transfusion of one of the other separate components of blood, such as plasma or platelets.

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  • Why do you need a blood transfusion? Why do you need a blood transfusion?

    Some of the main reasons why you might need a transfusion are listed below.

    • Severe anaemia. This is when your blood can't carry enough oxygen to meet the needs of your body. This can happen if you have fewer red blood cells than usual, or the amount of haemoglobin in each cell is less than normal.
    • During an operation. If you’re having major surgery, such as heart surgery, you may need a blood transfusion to replace blood that you have lost.
    • After an accident. If you have a serious accident, such as a road traffic accident, you may need a blood transfusion.
    • During pregnancy or birth. Some women bleed heavily after a miscarriage, or during or after labour. If this happens, you may need a blood transfusion.

    If you’re worried about having a blood transfusion, discuss it with your doctor.

  • What are blood groups? What are blood groups?

    Your red blood cells carry hundreds of different markers on their surface. These are called antigens, and they act as 'identity tags'. What blood group you are depends on which antigens you have on your red blood cells.

    There are two blood grouping systems that are the most important for matching your blood with someone else’s blood if you need a transfusion. These are the ABO system and the Rhesus (RhD) system. There are other blood group systems, but these are usually not as important for blood transfusion.

    The ABO system

    If your blood group is A then you have A antigens (tags) on your red blood cells. Blood group B means you have B antigens. If you’re group AB, then you have some of each antigen and if you’re blood group O, you have neither.

    In your blood you have antibodies, which will defend your body against what it sees as foreign antigens. So, for example, if you’re blood group A, you will have anti-B antibodies. This means that if you were given group B blood in a transfusion instead of blood group A, your body’s natural defences would attack the donated blood. This is very serious and is the reason why you will always be given blood that is compatible with your own blood group.

    The Rhesus (RhD) system

    If your blood group is RhD positive then you have RhD antigen on your red blood cells. RhD negative means you don't have it. About eight out of 10 people have the RhD antigen and are Rhesus positive. About two out of 10 people don’t have the RhD antigen and are Rhesus negative.

    If you’re RhD negative you shouldn't be given RhD positive blood because you may develop rhesus antibodies. This is particularly important if you’re a woman who is pregnant or you have the potential to become pregnant. If you’re rhesus negative and your baby is rhesus positive small amounts of blood can cross the placenta from your baby to you. When this happens your body produces antibodies which can destroy your baby’s rhesus positive red cells. This can cause your baby to become anaemic and fluid can leak into his or her tissues which can be very serious. The same problem can also affect any babies you have in the future. This is the reason why you have a blood test when you’re pregnant, to check your rhesus blood group and whether you have RhD antibodies.

    Your blood group is made up of your ABO group and your RhD antigen group together. So, for example, you may be A positive, O negative or B negative. Some blood groups are more common than others. Group O positive is the most common group and group AB negative is the least common.

  • Alternatives What are the alternatives to blood transfusion?

    A transfusion of blood from another person (a donor) is usually only given if there is no other alternative, because the risks sometimes outweigh the benefits. Some of the alternatives are listed below.

    • Cell salvage. This is where your blood that is lost during or after your operation is collected, and given back to you (autologous transfusion). You may have all of your blood given back or the blood may be processed and the plasma removed from it.
    • Autologous pre-donation or pre-deposit. This isn’t generally used in the UK but involves collecting some of your own blood a few weeks before a planned operation and then giving this back to you during or after your operation. It can be useful if you have a rare blood group.
    • If you have anaemia, it can be treated by ways other than blood transfusion; for example if you have iron deficiency you can take iron tablets.

    If you would like more information or want to discuss the alternatives to transfusion with donor blood, speak to your doctor or nurse looking after you.

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  • The procedure What happens during a blood transfusion?

    Before you have any type of blood transfusion you will have a blood sample taken. This is tested to see what blood group you are. Your blood is compared to the donor blood you will be receiving before you have the transfusion. This is to make sure it’s the right blood group and is called cross matching.

    Your nurse or doctor will ask you for your name and date of birth and check this against your hospital wrist band if you have one, and against the blood or blood product. This is to make sure you’re having the blood which has been specifically prepared for you.

    A cannula is put into a vein, usually in your arm. This is attached by plastic tubing to a bag of blood (called a unit of blood) which hangs on a stand beside you. It usually takes two to four hours to have one unit of blood (about 300 millilitres), although you can have it more quickly if you need it. If you’re having blood products, such as platelets, these are usually given in a shorter time because the volume is less.

    While you’re having the transfusion, your nurse will check on you regularly to make sure you’re feeling well, and to measure your blood pressure, temperature and heart rate.

  • Risks What are the risks of having a blood transfusion?

    As with every procedure, there are some risks associated with having a blood transfusion. We have not included the chance of these happening as they are specific to you and differ for every person. Ask your doctor to explain how these risks apply to you.


    Side-effects are the unwanted but mostly temporary effects you may get after having the procedure.

    During a blood transfusion, you may develop a fever, chills, itching or a rash. If this happens, you may be given medicines, such as paracetamol, to lower your temperature, and antihistamine to relieve any itching and a rash. If you do have side-effects your nurse or doctor may slow down your transfusion so that it goes into your body over a longer period of time.

    If you start to feel unwell at all during your blood transfusion, tell your nurse or doctor straight away.


    Complications are when problems occur during or after the procedure. Most people having a blood transfusion aren’t affected. Serious complications of blood transfusion are very rare. The main ones are listed below.

    • An immediate reaction to the donor blood. This can happen if the wrong blood is given by mistake. The symptoms of a reaction include fever, wheezing, feeling anxious and passing red-coloured urine. If this type of reaction does happen, your doctor or nurse will stop the blood transfusion and you will need emergency treatment.
    • Infection from bacteria in the donor blood. This can happen very quickly. You may have a high fever, a fast heart rate and shivering. If the infection isn’t treated, you may collapse. Your doctor will treat your symptoms and give you antibiotics to treat the infection.
    • Getting a viral infection from the donor blood. Although stringent measures are taken to prevent the transmission of viral infections, such as hepatitis and HIV, the possibility that this could occur can’t be fully ruled out.
    • Too much fluid in your body. This can happen if you have too many transfusions or if they are given too quickly. You may be short of breath with fast breathing and heart rate. If this happens, your doctor will treat your symptoms and give you medicines to help your body get rid of the extra fluid.
  • Where does the blood come from? Where does the blood come from?

    In the UK, blood is collected from healthy, unpaid volunteers. Many people donate blood regularly. Every donor has his or her ABO and Rhesus group checked when they give blood. If you donate blood, you will be asked to complete a health questionnaire each time, to make sure you’re healthy and able to donate. Every unit of blood that is collected from donors is checked for infectious diseases and stored until it’s needed by the National Blood Service, which is part of the NHS.

  • FAQs FAQs

    What can I do to reduce my need for a blood transfusion before having a planned operation?


    Eating a well-balanced diet in the weeks before your operation will increase your iron levels and reduce the need for you to have a blood transfusion. If you’re taking warfarin, aspirin or any other medicine that may affect how much you bleed, your doctor may ask you to stop taking these before your operation.


    Your body needs iron to make the oxygen-carrying pigment in your blood called haemoglobin. If you don’t have enough iron, you're more likely to be anaemic and need a transfusion. You can reduce the likelihood that you will need a blood transfusion by making sure you get enough iron in the weeks before your operation. You can do this by:

    • eating a well-balanced diet that includes foods which contain iron, such as meat, fish, cereals, beans and vegetables.
    • taking iron tablets – your doctor will tell you if you need to take iron tablets.

    If you’re taking medicines that affect how quickly your blood clots, your doctor may ask you to stop taking them for a few days before your operation. This is because they can cause you to bleed more. This includes medicines such as aspirin and warfarin. Only stop taking these medicines if your doctor tells you to.

    Are blood transfusions safe?


    You will only be given a blood transfusion if it's essential. The biggest risk from having a blood transfusion is that you will be given blood that was not intended for you. Your chance of getting an infectious disease from a blood transfusion is very low.


    Most people have a blood transfusion with no problems at all. However, there is a risk that you may be given blood from the wrong blood group. This happens very occasionally if a blood sample is taken from the wrong person, or a mistake is made when the blood is collected from the laboratory or when the transfusion is set up in hospital.

    Your nurse must follow very strict procedures when he or she gives you your blood transfusion, to make sure you get the blood that is meant for you. Your nurse or doctor will check your identity before taking the cross-match blood sample and should write your full details onto the bottle immediately. Before commencing the transfusion your nurse or doctor will ask you for your name and date of birth and check all the details on your identity bracelet and this should be repeated before each bag of blood is given to you.

    The risk of getting an infectious disease from a blood transfusion is very low. For example, the risk of getting HIV from a blood transfusion is one in five million, and the risk of getting hepatitis B is one in 500,000. This is because everyone that donates blood is carefully screened and tested to make sure that the blood they give is as safe as possible. All donated blood is tested for infectious diseases, such as hepatitis B, hepatitis C and HIV, before it's used.

    How can I donate blood?


    The National Blood Service holds regular blood donor sessions in the UK. Visit their website at to find out about sessions available in your local area.


    Before you give blood make sure you have eaten recently and have had enough to drink. Wear loose clothes on your top half to make giving blood easier.

    When you arrive at the blood donation session, you will be asked to read some information about giving blood and fill in a donor health questionnaire. This is to make sure that you haven't been exposed to anything infectious and that it's safe for you to donate blood. A nurse will take a drop of blood from your finger to make sure you’re not anaemic. If all is well, then you will be ready to donate blood.

    You will be asked to lie down on a bed and your nurse will look for a suitable vein in your arm to take the blood from. He or she will put a cuff, like a blood pressure cuff, around your upper arm to help the vein show up better. Your skin is carefully cleaned and a needle is put into your vein.

    Just under a pint of your blood is collected into a collection pack. This usually takes about 10 minutes. You may be given a small soft ball to squeeze in your hand. The movement helps the blood flow in your vein and makes it easier to collect. Your nurse will also take samples of blood from the blood you donate. This is used to check for infectious diseases.

    You may have other people around you giving blood and usually there aren't any screens between the beds. This helps the nurses see and monitor all the blood donors easily. A nurse will usually check on you regularly. If you do feel dizzy, faint or sick, let your nurse know immediately.

    After you have given your blood, you will have a short rest before having a drink and biscuit. The whole process shouldn't take more than an hour.

  • Resources Resources

    Further information


    • Longmore M, Wilkinson I, Davidson E, et al. Oxford handbook of clinical medicine. 8th ed. Oxford: Oxford University Press; 2010:342
    • McClelland DBL. Handbook of transfusion medicine. 4th ed, London: The Stationary Office; 2007
    • Blood group basics. NHS Blood and Transplant., accessed 30 May 2012
    • Pregnancy (rhesus negative women) – routine anti-D (review): understanding NICE guidance. National Institute for Health and Clinical Excellence (NICE), 2008.
    • Blood transfusions. Macmillan Cancer Support., published December 2011
    • Putting safety first. NHS Blood and Transplant., accessed 30 May 2012
    • Transfusion reactions. eMedicine., published January 2012
    • Will I need a blood transfusion? NHS Blood and Transplant., published July 2011
    • Giving blood. NHS Blood and Transplant., accessed 30 May 2012
    • Virtual tour of a blood donation session. NHS Blood and Transplant., accessed 30 May 2012
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