There are several different types of blood transfusion. Whether you need one depends on a number of factors.

These include:

• your health
• 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.

Platelets

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

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

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.

Surgical operations

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.