Blood transfusions

Some cancers or cancer treatments can cause anaemia, which is a low number of red blood cells. Blood transfusions are used to treat anaemia.

What is anaemia?

Anaemia is a low number of red blood cells. Many people with cancer have anaemia at some point. This is called being anaemic.

Anaemia can be caused by cancer, cancer treatment or both. The treatment could be chemotherapy, targeted therapy, immunotherapy, radiotherapy and sometimes surgery. Anaemia can also be caused by other things not related to cancer or cancer treatments.

Red blood cells contain a protein called haemoglobin (Hb), which carries oxygen around the body. If you do not have enough red blood cells, your body does not have enough haemoglobin. This reduces the amount of oxygen your body gets, which can make you feel very tired. You may also become breathless.

If you have symptoms of anaemia or are having cancer treatment, you will have a blood test called a full blood count (FBC). This checks the level of haemoglobin in your blood.

The normal haemoglobin level is:

  • 130-180 grams per litre of blood (g/L) for a man
  • 115-165 grams per litre of blood (g/L) for a woman.

These ranges can vary slightly between different hospital laboratories.

If your haemoglobin level is low, your doctors may recommend that you have a blood transfusion.

What is a blood transfusion?

Blood transfusions can treat anaemia. The blood you are given is from carefully screened blood donors. It is given by a drip into one of your veins.

The transfusion increases the number of red blood cells in your blood. This means that more oxygen can be carried around your body to your tissues and organs. This will increase your energy levels and reduce breathlessness.

Decisions about treatment

Before you have a transfusion, your doctor will explain the aims of the treatment to you. They may also give you information to read. You will be asked to give your permission (consent) for the hospital staff to give you a blood transfusion. Medical treatment can only be given with your consent.

You may decide not to have a blood transfusion. It is important to tell your doctor or nurse if you decide not to have treatment. They will record your decision in your medical notes.

You do not have to give a reason, but it can be helpful to tell the staff your concerns, so they can give you the best advice.

Jehovah’s Witnesses may choose not to have some types of blood products. If this affects you, talk to your doctor about other treatments or ways of managing your anaemia.

Having a blood transfusion

If you need a blood transfusion, your doctor or nurse will first take a sample of your blood to find your blood group. This is then closely matched to donor blood. This is called cross-matching.

The tests used to cross-match are done to:

  • make sure the blood is the best match for you
  • reduce possible side effects.

The blood for transfusion is stored in small plastic bags. Each bag is called a unit of blood. You will usually have 1 to 4 units of blood, depending on how anaemic you are.

Blood is given by a drip (infusion) into one of your veins. A nurse puts a short thin tube (cannula) into a vein in your arm or hand. This is then connected to a drip. If you have a central line or PICC line, your nurse can connect this to your drip instead.

Transfusion of each unit of blood can take up to 4 hours. If you are having 1 or 2 units of blood, you can usually have it at an outpatient clinic or day unit. Having a transfusion can take most of the day. If you need several units, you may need to stay in hospital overnight.

You should start to feel better within 24 hours of having the transfusion. But sometimes the benefits do not last long and you may need more transfusions.

Possible side effects of blood transfusions

Reactions to blood

Before and during the transfusion, your nurse will regularly check your temperature, pulse and blood pressure. This is to make sure you are not having a reaction to the blood.

Some people may have:

  • headaches
  • a slight rise in temperature
  • a skin rash.

These effects can be reduced by taking drugs such as paracetamol or slowing the transfusion down.

Severe side effects from blood transfusions are rare because blood is cross-matched first. If you have any severe side effects, the nurse will stop the transfusion and quickly treat any symptoms. Tell your nurse straight away if you have any chest or back pain, feel sick or are short of breath during your transfusion.

If you have any problems after you get home, contact the hospital.

Fluid overload

Sometimes, the amount of fluid given in a blood transfusion can put a strain on the heart. If you have heart problems, it may be more difficult to get rid of any extra fluid. Your doctor may give you medicine (a diuretic) for this, to help you pass the extra fluid out in your urine (pee).

Tell your doctor or nurse straight away if you have puffiness or swelling in your hands or feet, or feel short of breath.

Iron overload

Red blood cells contain a small amount of iron. If you have lots of blood transfusions over many months, iron can build up in your body. This is called iron overload.

If you are at risk, you can have treatment to stop it happening. Your doctor or nurse can explain more about this.

Are blood transfusions safe?

Some people worry that the blood they are given may be infected by disease. People who donate blood are carefully screened for infection or viruses such as hepatitis or HIV. This is to make sure the donations are as safe as possible.

All donated blood is tested in the laboratory for infection. Very rarely, there may be an infection in the blood that is not found by these tests. But the risk of being given infected blood is extremely small.

If you have any concerns about receiving a blood transfusion, talk to your doctor or specialist nurse.

Checking your details

When your blood is cross-matched, the nurse will record your name, date of birth, and identification number on the sample.

Before you have a blood transfusion, the nurses will put an identification band on your wrist with all of your details on. They check your details, including your blood group, several times before they give you a blood transfusion, even when they have treated you many times. This is to make sure you are getting the blood that has been matched for you. The nurses will check your identification band carefully, and also ask you to give your full name and date of birth before each bag of blood is given.

Irradiated blood

Some people may need to have blood products that has been treated with irradiation.

You may need irradiated blood products if you have had:

Your doctor will tell you if this applies to you.

Irradiated blood products lower the risk of the donated cells reacting against your own. The radiation will not damage the blood product or make you radioactive. Your doctor will record in your medical notes if you should only have irradiated blood products.

They will also give you a special card to carry, in case you are treated at another hospital. Keep this card with you at all times and remind your hospital team that you need irradiated blood or platelets.

About our information


  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.