Bone marrow is a spongy material that fills some of the bones and produces the cells (called stem cells) which develop into the three main different types of blood cells:

• red blood cells, which carry oxygen to all cells in the body


• white blood cells, which are essential for fighting infection


• platelets, which help the blood to clot and control bleeding

To tell whether the bone marrow is affected, a needle is put into the bone of the hip and some of the marrow is drawn out and taken for examination. A small sample of bone may also be taken (trephine biopsy). This test is done under heavy sedation, to avoid any discomfort to your child.