What are stem cells and bone marrow?

There are two different types of stem cell transplants:

  • high-dose treatment with stem cell support
  • allogenic (donor) stem cell transplants.

To understand these treatments, it first helps to learn how the bone marrow and stem cells work.

Stem cells are blood cells at their earliest stage of development. All blood cells develop from stem cells. The full name for stem cells in the blood and bone marrow is haematopoietic stem cells, but in this booklet we call them stem cells.

Bone marrow is a spongy material inside the bones – particularly the bones of the pelvis. The bone marrow is where stem cells are made.

Most of the time, almost all of your stem cells are in the bone marrow. There are usually only a very small number in the blood. Stem cells stay in the bone marrow while they develop into blood cells. Then, once they are fully mature, the blood cells are released into the bloodstream.

The three main types of blood cells are:

  • Red blood cells – These contain haemoglobin (Hb), which carries oxygen to all cells in the body.
  • White blood cells – These fight infection. There are several types of white blood cell. The two most important are neutrophils and lymphocytes.
  • Platelets – These help blood to clot and prevent bleeding.

Illustration of bone marrow
Illustration of bone marrow

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The levels of blood cells in your blood are measured in a blood test called a full blood count (FBC). It’s often just called a ‘blood count’.

The figures below are a guide to the levels usually found in a healthy person.

Type of blood cellLevels found in a healthy person
Red blood cells (Hb)130–180g/l (men)
115–165g/l (women)
Platelets150–400 x 109/l
White blood cells (WBC)4.0–11.0 x 109/l
Neutrophils2.0–7.5 x 109/l
Lymphocytes1.5–4.5 x 109/l

These figures can vary from hospital to hospital. Your doctor or nurse can tell you what levels they use. They can also vary slightly between people from different ethnic groups.

The figures might look complicated when they’re written down, but in practice they’re used in a straightforward way. For example, you’ll hear doctors or nurses saying things like ‘your haemoglobin is 140’ or ‘your neutrophils are 4’.

Most people with cancer or leukaemia soon get used to these figures and what they mean. But you can always ask your medical team to explain if you’re not sure.

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