Background

Red blood cells comprise the majority of blood cells in the circulation, and one of their main functions is to carry oxygen from the lungs to all cells, tissues, and organs in the body. Oxygen is carried inside the red blood cell combined to an iron containing protein called "haemoglobin". Red blood cells have no nucleus and are shaped like a biconcave disc or "doughnut-shaped", and are able to curl up and squeeze through the smallest of blood vessels.

The number of red blood cells normally in the blood varies, and is higher in men than women. New born babies have a higher red cell count than adults.

If there is a higher number of red blood cells in the circulation than normal then a person is said to have erythrocytosis or polycythaemia. The opposite situation can occur, where there is a lower level of red blood cells than normal, and this condition is referred to as "anaemia".

Raised red blood cell counts can be found incidentally in people with no symptoms, in the early stages of polycythaemia.