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.

Allergic reaction

Having an allergic reaction to the donated blood is an uncommon complication of a blood transfusion. In 2011, there were 180 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:

  • raised, red, itchy skin rash (urticaria)
  • swelling of hands, arms, feet, ankles and legs (oedema)
  • dizziness
  • headaches

Less common symptoms include:

  • high temperature (fever) of or above 38ºC (100.4ºF)
  • chills
  • shivering

These types of reactions can usually be successfully managed by slowing down or stopping the transfusion and treating the symptoms with antihistamines (medication for allergies) 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 2011, there were 33 suspected 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:

  • chills
  • abdominal cramps
  • shortness of breath
  • vomiting
  • diarrhoea 

Anaphylaxis is usually treated with an injection of a type of medication called adrenaline.

Fluid overload

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.

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 71 cases of fluid overload in the UK during 2011.

Lung injury

An uncommon but very serious risk associated with blood transfusions is transfusion-related acute lung injury (TRALI).

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.

Acute haemolytic transfusion reaction

An acute haemolytic transfusion reaction (AHTR) is when the immune system reacts to the donated blood and begins attacking the blood cells.

One cause of AHTR is when a person is mistakenly given the wrong blood type. However, AHTR can occasionally occur when all the procedures associated with a blood transfusion have been correctly followed.

During AHTR, the immune system attacks the donated blood cells, triggering a range of symptoms that usually develop very quickly after the transfusion and rapidly get worse.

Symptoms of AHTR include:

  • anxiety
  • shortness of breath
  • high temperature (fever) of 38ºC (100.4ºF) or above
  • chills
  • facial flushing

People with AHTR may go into shock (a seriously reduced blood flow), which can cause the following symptoms:

  • cold, clammy skin
  • low blood pressure
  • nausea
  • vomiting

A person with AHTR may develop acute (sudden) kidney failure. AHTR is a medical emergency that usually requires admission to an intensive care unit (ICU) where medication and fluids are administered to improve blood flow.

During 2011, there were 10 cases of AHTR in the UK.

Bacterially contaminated blood

Despite every effort being made to keep donated blood sterile (germ-free), bacteria can occasionally develop in donated blood. 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:

  • high temperature
  • chills
  • a fast heartbeat
  • fast breathing
  • cold, clammy skin
  • changes in mental states, such as confusion

Cases of sepsis usually need to be treated with injections of antibiotics. See treating sepsis for more information.

There were no cases of bacterial infections associated with contaminated blood in the UK in 2011.

Viral contaminated blood

It is 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 2.5 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.

Page last reviewed: 24/01/2013

Next review due: 24/01/2015