Erythrocytosis (often referred to as polycythemia) is an increase in the number of red blood cells in the bloodstream. (Polycythemia varies from erythrocytosis in that polycythemia may also refer to an increase in white blood cells or platelets.) Primary erythrocytosis (polycythemia vera) is a disease in which the blood-producing cells in the bone marrow develop and reproduce abnormally. It has been reported in cats. Red blood cell production is dramatically increased, and levels of the hormone that stimulates development of red blood cells (erythropoietin) are low or normal. In secondary erythrocytosis (secondary polycythemia), red blood cell production increases in response to increased erythropoietin levels. This may be seen in severe lung disease, heart abnormalities, abnormalities of blood circulation, certain kidney diseases, and some types of tumors. Cats with hyperthyroidism (a disease caused by excessive production of thyroid hormone) or acromegaly (a disease caused by excessive production of growth hormone) may also have erythrocytosis that is too mild to cause any signs.
Your veterinarian will use tests of blood and urine to help diagnose erythrocytosis. In some cases, x-rays and other tests may also be required. Signs of the disorder include red mucous membranes, bleeding tendencies, the passing of large amounts of urine, excessive thirst, seizures or behavioral changes, lack of coordination, weakness, and blindness. Treatment of erythrocytosis includes removing red blood cells by withdrawing blood through a catheter placed in a vein, then replacing the lost blood with fluids. Drugs such as hydroxyurea may also be added to the treatment. In some cases, the underlying disease must be treated.
Also see professional content regarding polycythemia.