views updated

polycythaemia (poli-sy-theem-iă) n. an increase in the packed cell volume (haematocrit) in the blood. This may be due either to a decrease in the total volume of the plasma (relative p.) or to an increase in the total volume of the red cells (absolute p.). The latter may occur as a primary disease or as a secondary condition in association with various respiratory or circulatory disorders and with certain tumours. p. vera (p. rubra vera, erythraemia, Vaquez-Osler disease) a disease in which absolute polycythaemia is often accompanied by an increase in the numbers of white blood cells and platelets. Symptoms include headache, thromboses, cyanosis, plethora, and itching.