This information is about a rare type of chronic lymphocytic leukaemia (CLL) , known as hairy cell leukaemia. It should ideally be read with our information about CLL which discusses some of the issues facing people living with leukaemia. Blood cells Hairy cell leukaemia Causes Signs and symptoms How it is diagnosed Treatment After treatment Clinical trials Support References Blood cells Leukaemia is a general term for an overproduction of white blood cells. To understand the effect of leukaemia on the body, it helps to know about the normal process of blood cell production. Blood cells all follow the same pattern of development. They form in the bone marrow (the spongy part inside some bones) and then pass into the blood. There are three types of blood cell: Red blood cells , which contain haemoglobin (Hb) to carry oxygen around the body Platelets , whi...