What is polycythaemia?
It can be hard to imagine that health problems might arise from having too much blood. But in polycythaemia this is exactly what happens. Polycythaemia happens when there are too many red blood cells in the circulating blood. This makes the blood ‘thicker’, which can have the effect of ‘slowing up’ the circulation. Red blood cells carry oxygen and sometimes the body makes excessive numbers in an attempt to compensate for situations where there is a lack of oxygen. Such situations include living at high altitudes (where there is less oxygen in the air), some heart diseases and lung problems. Many cigarette smokers have a mild degree of this type, known as ‘secondary’ polycythaemia. But sometimes polycythaemia occurs in the absence of such underlying problems. In these cases, known as polycythaemia vera, there is an abnormality of the JAK 2 gene that helps control production of red blood cells in the bone marrow. This damage is not passed on to children — polycythaemia vera is not an inh
