If someone has experienced substantial bleeding during surgery or because of an accident, their blood volume may be too low to effectively carry oxygen around the body. In these circumstances, a blood transfusion – giving the person blood donated by someone else – can be lifesaving.
All donated blood is screened for blood-borne diseases such as hepatitis and HIV.
The four different blood types are A, B, AB and O, and each type is either Rh-positive or Rh-negative. (A person's blood type used to be called their 'Rhesus type' but now we simply say 'Rh type’.) When a transfusion is given, it is important for a person to receive blood of a compatible (or matched) ABO and Rh group. However, in an emergency, if the required blood type is not known and there is not enough time to find out, a person may be given group O negative red blood cells. That is why O negative is known as the universal blood type and is in higher demand than any other blood type.
Blood carries oxygen and nutrients
All cells in the body need oxygen and nutrients, and to have their waste taken away. These are the main roles of the circulatory system. Using the network of arteries, veins and capillaries, blood ferries carbon dioxide to the lungs (for exhalation) and picks up oxygen. From the small intestine, the blood gathers food nutrients and delivers it to every cell.
Blood consists of:
- red blood cells – to carry oxygen
- white blood cells – that make up part of the immune system
- platelets – needed for clotting
- plasma – liquid in which blood cells, nutrients and wastes float.
When blood transfusion is needed
Some of the different conditions that require transfusion of blood or blood products include:
- blood loss – that is severe enough to affect blood volume and circulation
- severe anaemia – where the blood can’t carry sufficient oxygen to the cells of the body
- bleeding – too few platelets can lead to spontaneous bleeding.
Different types of blood collection
The main ways in which blood is collected include:
- whole blood (homologous) collection – whole blood is collected from the donor, separated into different components and given as a transfusion to people with compatible blood types
- apheresis collection – only some components, either plasma or platelets, are taken from the blood of the donor. A machine centrifuges the cells and gives the red cells, or red cells and plasma, back to the donor.
Very uncommon ways in which blood is collected include:
- autologous collection – prior to a scheduled operation or transfusion, a person donates blood specifically for their own use.
- directed or designated collection – prior to a scheduled transfusion, a person requests that only blood collected from family members or friends be used for transfusion.
Autologous and directed donations are now discouraged except where a medical specialist believes there is a case for ‘special need’. Contrary to what some people believe, these blood donations share the same small risks normally associated with homologous donations.
Occasional complications caused by receiving a blood transfusion can include:
- fluid overload – this can be lessened by introducing the donated blood slowly
- allergic reaction – the person’s immune system treats the donated blood products as a threat. Symptoms include itching, dizziness, headache and difficulties in breathing. Severe allergic reactions can sometimes be life threatening
- haemolytic reaction – this happens if the person is given the wrong type of blood. The transfused red blood cells are destroyed or broken down. Symptoms include a feeling of pressure in the chest, back pain and difficulties in breathing. Haemolytic reaction can sometimes be life threatening
- transfusion related acute lung injury (TRALI) – where the transfused blood causes a reaction that leads to blockages in the blood vessels in the lungs. Symptoms include difficulty in breathing and low blood oxygen levels. This can sometimes be life threatening.
A blood donor needs to:
- be aged between 16 and 70 years
- weigh at least 45 kg
- be in good health, including normal temperature and blood pressure
- meet guidelines designed to protect the donor and the people who will receive their blood.
Where to get help
- Your doctor
- Your surgeon
- Australian Red Cross Blood Service Tel. 13 14 95 – to make an appointment to donate blood or for more information
This page has been produced in consultation with and approved by:
Australian Red Cross Blood Service
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