Bone marrow transplants are often needed when a person's own bone marrow has been

damaged and can no longer produce normal blood cells.

Any disruption to the production of blood cells can be very serious, particularly if:

• you do not have enough red blood cells - your body will be starved of oxygen, you will feel tired and faint and your organs may be damaged
• you do not have enough white blood cells - you will have a much higher risk of developing a serious infection
• you do not have enough platelets - you will bleed and bruise more easily

Some of the conditions that can affect blood and bone marrow are described below.

Bone marrow failure

The continuous process of producing blood cells and platelets to replace old cells is an essential part of healthy life. In adults, this reproduction process only occurs within bone marrow.

Therefore, a bone marrow transplant may be needed in cases where a person's bone marrow fails (severe aplastic anaemia). This may be due to an inherited condition, such as a rare type of anaemia, or as the result of an acquired condition, such as hepatitis B, Epstein-Barr virus (the virus that causes glandular fever) or parvovirus B19.

Leukaemia

Leukaemia is cancer of the white blood cells. The white blood cells replicate in an uncontrollable manner and do not develop any infection-fighting properties.

The cancerous cells can quickly spread through your bloodstream, resulting in a lack of room for red blood cells and platelets.

This can lead to the symptoms of anaemia and increases your risk of serious infection. You will also bleed and bruise more easily.

There are a number of different types of leukaemia where a bone marrow transplant may be needed. These are:

• acute lymphoblastic leukaemia
• acute myeloid leukaemia
• chronic lymphocytic leukaemia
• chronic myeloid leukaemia 

Non-Hodgkin's lymphoma

Non-Hodgkin's lymphoma is also a cancer of the white blood cells. However, unlike leukaemia it spreads through the lymphatic system rather than the bloodstream.

The lymphatic system is a series of connected glands (nodes) that are located around your body. It is an important part of the immune system which is your body's natural defence against infection and illness.

Read more about non-Hodgkin's lymphoma.

Genetic blood and immune system disorders

There are number of blood disorders where mutations (alterations) in your genes result in the blood cells not developing normally. These include sickle cell anaemia and thalassaemia. Both conditions interfere with the production of red blood cells.

Immune system disorders can include a wide range of immunodeficiencies and some other genetic conditions.