You might have a bone marrow transplant if If you have some types of cancer, like leukaemia, if chemotherapy cannot kill all the white blood cells that don't grow properly.

You may also need a bone marrow transplant if you have a genetic condition that stops your blood cells from growing normally, like thalassaemia or sickle cell anaemia.

If you have had an organ transplant and your body rejects your new organ, you may have a bone marrow transplant if immunosuppressants can’t stop the rejection. If the new bone marrow is taken from the same donor that you got your new organ from, then transplant rejection is much less likely.

You will receive healthy stem cells from a donor who has the same, or very similar, type of stem cells as you. This will very often be someone from your own family – if you have a brother or sister, there is a 25% chance that their stem cells will be an exact match with yours.

If no one in your family matches with you, then the doctors will find someone else who does. Lots of people donate stem cells, but you might have to wait quite a while before your right match is found.

It’s very important that you and the donor have the same type of stem cells. If you have a different type, your immune system might think they are foreign bodies and reject them. Or, the opposite could happen – the donated stem cells might think your body is a foreign object and attack it, leading to something called graft versus host disease (GVHD).

Before you have a bone marrow transplant, your doctor will examine you to make sure that you are as well as you can be, so that you can recover as quickly as possible from the operation. You may have scans to check that your liver, heart and lungs are working properly. You will be more likely to get infections than other kids afterwards, so the doctor will make sure you don’t already have any infections before you have the operation.

After you have been checked over, the unhealthy blood cells are completely cleared out of your bone marrow by some extra strong chemotherapy. This will probably take between 4 and 7 days, and you will likely need to stay in hospital for this time. You will have all your chemotherapy medicine through a central line that is put into a big vein near your heart, instead of having it through painful injections each time!

You will probably have your transplant 1 or 2 days after your chemotherapy has finished. The donated stem cells are passed into your body through your central line. It normally takes about an hour from start to finish, and you will be awake the whole time!

No. The donated stem cells are passed into your body through a central line and it is not painful at all.

The chemotherapy that is used to clear out your bone marrow is very strong, so you will probably get some side effects. The side effects you are most likely to get include:

• Being sick
• Feeling sick
• Diarrhoea (runny poo)
• Not feeling hungry
• Ulcers in your mouth
• Tiredness
• Rashes on your skin
• Losing your hair

The side effects can last for a few weeks after the chemotherapy has finished, but the mouth ulcers and skin rashes will probably go away when the new stem cells start making new blood cells. Your hair will probably grow back in 3 to 6 months.

GVHD (graft versus host disease) is something that you can get if the donated stem cells think the rest of your body is foreign and start making antibodies to attack it. There are two types of GVHD.

The first type is called acute GVHD, which you normally get within 3 months of having your transplant. The symptoms of acute GVHD include:

• Red spots on your hands, feet, and face
• A rash across your body
• Blisters from the rash
• A fever (high temperature)
• Bloody, or watery, diarrhoea (runny poo)
• Stomach pains
• Jaundice (a liver problem that can cause your skin to go a yellowish colour)

The second type is called chronic GVHD. This usually develops about 3 months after your transplant. You can have the symptoms all the time, or you might get them on and off, for several years. The symptoms include:

• An itchy, dry rash that can spread over your whole body
• A dry and sensitive mouth
• Dry eyes
• Hardening skin
• Losing your hair

If the GVHD is very serious, it can affect the way your liver or lungs work.

You can have medicines called immunosuppressants to treat GVHD. You may often also take corticosteroids as well. The medicines work by stopping the donated stem cells from releasing the antibodies that are attacking the rest of your body.

After your transplant, you have to wait for the stem cells to find their way to your bone marrow and start making new blood cells. This usually takes about 15-30 days.

You will need to have regular blood transfusions while you are waiting, as you will have a low number of red blood cells.

There is also a high chance of getting an infection. This is because you will have a low number of white blood cells, and because the chemotherapy you had has weakened your immune system. This means that you will have to stay in hospital in a special germ-free area, and you may also be given some antibiotics to stop you getting infections. Your family and friends will still be able to come and see you, but they will probably have to wear masks, gowns and gloves to make sure they don’t pass any infection on to you.

Even when your new stem cells have started making blood cells, you will still feel very weak and tired because of the chemotherapy. You will also still be prone to infection - it can take a few years for your immune system to get back to normal. You might also be given immunosuppressants to stop you getting GVHD. This means that you may have to stay in hospital for up to 3 months after your operation.

When you start playing with your friends again and go back to school, you must take special care not to pick up infections. Your doctor will be able to give you advice on how to do this.

If you have any other questions, you can ask your doctor, or chat to other people about bone marrow transplants in the Medikidz forums and virtual world, Mediland.

Or you can have a look at the NHS Choices article on bone marrow transplants.