Polycythemia is an abnormal increase in the number or concentration of circulating red blood cells (“RBCs”). Polycythemia is also known as erythrocytosis (another name for red blood cells are “erythrocytes”). The signs and treatment of polycythemia vary greatly depending on the cause of the condition. There are two main types of polycythemia in cats, relative and absolute. These can further be broken down into primary and secondary absolute polycythemia. It is important to determine which type is involved in a given animal so that treatment can be tailored appropriately.
Relative polycythemia is typically treated by inpatient rehydration using intravenous or subcutaneous fluids, the selection of which depends upon the functional status of the cat’s kidneys and other organ systems. A veterinarian can easily increase a cat’s overall body fluid levels by well-monitored fluid therapy. Keeping the cat as calm as possible can facilitate the rehydration process. Once the animal’s fluids levels return to normal, the condition should be resolved.
Absolute Polycythemia - Primary
Primary absolute polycythemia is the result of an uncommon but chronic bone marrow disorder in cats. The cause is not well understood. Basically, the blood becomes too thick, because the solid components are elevated while the fluid components remain relatively normal. Initial treatment of absolute primary polycythemia is to reduce the viscosity of the blood by reducing the number of circulating RBCs. This is accomplished through therapeutic phlebotomy – a procedure where a predetermined amount of blood is removed from one of the cat’s central veins. To prevent the patient’s blood pressure from dropping dramatically because of rapid blood loss, veterinarians usually simultaneously administer a roughly equivalent volume of saline through a different catheter. Phlebotomies sometimes are called “bleeding the animal” and may need to be repeated periodically. If the underlying condition is severe, certain medications can be administered to suppress red blood cell production by the bone marrow. Discuss the consequences of these treatments with your veterinary professional.
Absolute Polycythemia – Secondary
Secondary absolute polycythemia occurs when the kidneys produce too much erythropoietin (“EPO”), a hormone that regulates red blood cell production through a different mechanism than that causing primary absolute polycythemia. Normally, the kidneys in cats make and release EPO in response to hypoxia, which is an insufficient availability of oxygen to body tissues. A number of conditions can cause inadequate oxygen supply, such as adaptation to high altitude, insufficient production of EPO by the kidneys due to cancer, cysts or other forms of renal disease, hyperthyroidism, hyperadrenocorticism, heart or lung disease or other causes of circulatory insufficiency. Regardless of cause, secondary absolute polycythemia is the result. In order to treat secondary absolute polycythemia, the cause of the condition first must be diagnosed and controlled. In some cases, especially if the cat’s signs of polycythemia are severe, periodic therapeutic phlebotomies also will be recommended.