Question

What are red blood cells for and can you have too many of them?

Answer

Red blood cells carry haemoglobin, which carries oxygen in the blood, and so to all body tissues. The oxygen gets there as the blood circulates through the lungs.

There are certain diseases in which the haemoglobin concentration and red blood cell mass are increased.

One of these is polycythemia vera, a rare disease of unknown cause. The symptoms are due to an increased volume of blood circulating in the body and the blood being more sticky than usual. The main symptoms are weakness, headache, light-headedness, visual disturbances, fatigue and shortness of breath.

Heavy, long term smokers can have an increased red blood cell mass which will cause similar symptoms. This is reversible if they stop smoking.

Certain types of chronic lung disease and heart abnormalities may also lead to this. Some tumours also cause an increase in red blood cell mass.