Having too many red blood cells is called erythrocytosis. In animals with erythrocytosis, the blood can become too thick, making it hard for the heart to pump circulating blood and to deliver oxygen to cells throughout the body. Erythrocytosis (often called polycythemia) is an increased number of red blood cells.
In primary erythrocytosis (also called polycythemia vera), blood‑producing cells in the marrow grow and divide abnormally, causing red blood cell production to rise sharply, even though erythropoietin levels are normal or low. Primary erythrocytosis has been reported in cats.
In secondary erythrocytosis, red blood cell production increases because of high erythropoietin levels. This occurs with severe lung disease, heart defects, abnormal blood circulation, some kidney diseases, and certain tumors. Cats with hyperthyroidism or acromegaly might also have mild erythrocytosis without obvious symptoms.
Erythrocytosis is diagnosed via blood and urine tests and sometimes via x‑rays or other imaging techniques. Symptoms can include very red mucous membranes, a tendency to bleed, increased thirst and urination, seizures, behavioral changes, poor coordination, weakness, and occasionally blindness.
The treatment for erythrocytosis is to remove excess red blood cells by drawing blood and replacing fluid, and to give the patient drugs such as hydroxyurea to decrease red blood cell production. For secondary erythrocytosis, treating the underlying disease is also essential.
