The blood

Blood is made up of blood cells, which float in a liquid called plasma. Blood cells are made in the bone marrow. This is a spongy material that’s found in the middle of our bones, particularly in our pelvis and backbone (spine). Normally, millions of new blood cells are made every day to replace old and worn-out blood cells.

All our blood cells are made from cells called stem cells. There are two types of stem cell:

• lymphoid stem cells, which make white blood cells called lymphocytes
• myeloid stem cells, which make all the other types of blood cells: red blood cells, platelets, and white blood cells called granulocytes.

How cells grow

In the bone marrow, the stem cells divide and grow to form fully developed (mature) red blood cells, platelets and white blood cells.

To begin with, new blood cells are immature. They don’t look like red blood cells, platelets or white blood cells, and they can’t yet do the jobs they’re supposed to do. These immature cells are called blast cells. Usually, blast cells stay in the bone marrow until they have matured into red blood cells, platelets or white blood cells.

These are then released into your blood to carry out different functions:

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

The levels of these cells in your blood are measured in a blood test called a full blood count (FBC). The figures below are a guide to the levels usually found in a healthy person.

Type of blood cell	Levels found in a healthy person
Haemoglobin (Hb)	13-18g/dl (men) 11.5-16.5g/dl (women)
Platelets	150-400 x 109/l
White cells (WBC)	4.0-11.0 x 109/l
Neutrophils	2.0-7.5 x 109/l

These figures can vary from hospital to hospital. Your doctor or nurse will be able to 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 14’ or ‘your neutrophils are 4’. Most people with AML soon get used to these figures and what they mean. But remember, you can always ask your medical team for further explanation if you need it.