Having a bone marrow transplant is a complicated five-stage process.

The five stages are:

• physical examination – to assess your general level of health
• harvesting – the process of obtaining the stem cells to be used in the transplant
• conditioning – preparing your body for the transplant
• transplanting the stem cells
• recovery period – during which you'll be monitored for any complications or side effects

The five stages are described in more detail below.

Physical examination

You'll have a thorough physical examination before a stem cell transplant. How healthy you are before the transplant will play a big part in your recovery.

As part of the examination, you may have some scans to check the condition of internal organs, such as your liver, heart and lungs.

Some of the medication used in the conditioning and recovery process can occasionally cause problems with your organs, so it's important to know how well they're functioning beforehand.

After the transplant, you'll have an increased risk of developing an infection, so it's important to make sure you don't have any underlying infections.

If you have a cancer-related condition, you may need to have a biopsy. A small sample of cancerous cells will be removed and checked in a laboratory.

The results of  the biopsy will show whether your cancer is in remission (under control) and whether there's a high risk of it returning after your transplant.

Harvesting stem cells

After you've had a physical examination, the stem cells will need to be harvested.

The method most commonly used in adults involves removing blood from the body, separating stem cells from the other cells in the blood and then returning the blood to the body.

An alternative method is to collect the bone marrow itself by removing stem cells from the hip bone using a special needle and syringe. This may be recommended for certain conditions that require a transplant, or if the donor is a child.

Autologous transplantation

It may be possible to use your own stem cells, providing they're suitable. This is known as an autologous transplantation. They can be harvested using either method described above.

If your bone marrow is being extracted, a needle will be used to remove around a litre of bone marrow. It will usually be removed from your hip bone, under general anaesthetic.

The procedure is low risk, but the area where the needle is inserted may be painful afterwards. The harvesting process may sometimes need to be carried out a number of times before enough bone marrow is obtained.

After being extracted, your stem cells may need to be treated with radiation or chemotherapy to ensure there are no cancerous cells left.

Allogeneic transplantation

If your own stem cells aren't suitable, stem cells will be harvested from a healthy donor. This is known as allogeneic transplantation.

In around 30% of cases, a family member, such as a brother or sister, is a suitable donor. The other 70% of people who need a bone marrow transplant have to rely on finding a suitable donor through the British Bone Marrow Registry (BBMR).

It's very important that the BBMR continues to recruit more donors, particularly from ethnic minority communities. Finding a suitable stem cell match is often difficult due to a lack of volunteers. In particular, there's a shortage of donors from African, African-Caribbean, Asian, Jewish, eastern European and Mediterranean communities.

The more people who register, the more chance there is of finding a matching tissue type for someone who needs a transplant. When a suitable donor is found, their identity and location, and those of the patient, remain confidential.

The methods of harvesting cells from a healthy donor are similar to those used for an autologous transplant (see above).

For four days prior to the transplant, the donor will be given medication to stimulate the production of stem cells in their blood. On the fifth day, they'll have a blood test to check they have enough circulating stem cells.

They'll then be connected to a cell-separator machine. A general anaesthetic isn't needed, which means the harvesting can be carried out as an outpatient procedure.

Blood is removed through a vein in one arm and passed through a filtering machine, to separate the stem cells from other blood cells. It's then returned to the body through a vein in the other arm.

If the number of cells obtained is insufficient, the donor may be asked to return on the sixth day to make another donation. The procedure usually requires about two sessions lasting two to three hours on successive days.

Removal of bone marrow from the hip bone is carried out in hospital, under general anaesthetic, using a needle and syringe.

Although it's not a surgical operation, some marks from the needle will be left on the skin. There may also be some discomfort where the needle is inserted.

The donor will need to stay in hospital for up to 48 hours and have an at-home period of recovery lasting up to five days.

Conditioning

As part of your conditioning, you'll need to be given a range of medicines, meaing a tube will be inserted into a large vein near your heart. This is known as a central line and is used instead of many (often painful) injections.

The conditioning process involves using high doses of chemotherapy and sometimes radiation. It's carried out for three reasons:

• to destroy the existing bone marrow cells to make room for the transplanted tissue
• to destroy any existing cancer cells
• to stop your immune system working, which reduces the risk of the transplant being rejected 

The conditioning process usually takes between four and seven days. You'll probably need to stay in hospital throughout the procedure. Side effects from chemotherapy are common and include:

• nausea (feeling sick)
• vomiting
• diarrhoea 
• loss of appetite
• mouth ulcers 
• tiredness
• skin rashes
• hair loss 

Side effects can last for several weeks after conditioning has finished, although mouth ulcers and skin rashes should stop once the transplanted tissue begins to produce new blood cells. Hair usually grows back within three to six months.

Two less common, but potentially very serious, side effects of the conditioning process are lung damage and a condition called veno-occlusive disease.

Lung damage or a lung infection can be treated with oxygen, antibiotics and other treatments. Steroids (strong medication) may also be given to dampen potentially dangerous immune reactions.

Veno-occlusive disease causes the blood vessels in your liver to swell, stopping it from removing waste products from your body. This can cause abdominal pain, jaundice (yellowing of the skin and whites of the eyes) and weight gain.

Veno-occlusive disease can be treated with medicines to help prevent blood clots, as well as using blood transfusions and reducing the amount of salt in your diet.

Read more about the risks of bone marrow transplants.

The transplant

It's usually possible to carry out the transplant one or two days after conditioning has finished.

The donated stem cells will be passed into your body through the central line. This process can take anywhere from half an hour to several hours to complete, depending on the type of blood cells being used.

The transplant won't be painful and you'll be awake throughout the procedure.

Recovery

You may feel weak after the transplant, and you may experience vomiting, diarrhoea and/or a loss of appetite.

To prevent malnutrition (a lack of essential nutrients), you'll need to have nutritional support, with high-protein fluids taken by mouth or through a tube running from your nose to your stomach.

The first stage of the recovery process involves waiting for the stem cells to reach your bone marrow and start producing new blood cells. This is known as engraftment and usually occurs 15-30 days after the transplant takes place.

During this period, you'll need to have regular blood transfusions, as you'll have a low number of red blood cells.

Your risk of developing an infection will also be increased, because you'll have a low number of white blood cells. This means that you'll need to stay in hospital, in a germ-free environment.

You may be allowed visitors, but they may have to wear surgical gowns and hats to prevent infection. Antibiotics may also be used to either prevent or treat infections.

Once engraftment has occurred, your bone marrow will begin to produce blood cells. However, you'll still be very weak from the effects of the chemotherapy.

You'll still have a high risk of developing an infection, as it can take as long as one to two years for your immune system to return to full strength.

You may also be given medicines that stop your immune system from working (immunosuppressants), to prevent graft versus host disease (GvHD).

Many people are well enough to be discharged from hospital between one and three months after undergoing a bone marrow transplant. However, if you develop complications, such as an infection, you may not be able to leave hospital for more than three months after the transplant.