Characterized as an abnormal increase in the amount of red blood cells in the circulatory system, polycythemia is a rather serious blood condition. More specifically, it entails an increase in packed cell volume (PCV), hemoglobin concentration (the red pigment of the blood cell), and in red blood cell (RBC) count, above the reference intervals, due to a relative, transient, or absolute increase in the number of circulating red blood cells. Polycythemia is classified as relative, transient, or absolute. Relative polycythemia develops when a decrease in plasma volume, usually caused by dehydration, produces a relative increase in circulating RBCs. Transient polycythemia is caused by splenic contraction, which injects concentrated RBCs into the circulation in a momentary response to epinephrine, the hormone that reacts to stress, anger, and fear. Absolute polycythemia is characterized by an absolute increase in the circulating RBC mass, as a result of an increase in bone marrow production. Absolute polycythemia, typified by increased RBCs in the bone marrow, can be primary or secondary to an increase in the production of EPO. Primary absolute (called polycythemia rubra vera) is a myeloproliferative disorder characterized by the excessive, uncontrolled production of RBCs in the bone marrow. Secondary absolute polycythemia is caused by a physiologically appropriate release of EPO resulting from chronic hypoxemia (lack of oxygen), or by inappropriate and excessive production of EPO or EPO-like substance in an animal with normal blood oxygen levels. Polycythemia can affect both dogs and cats. If you would like to learn more about how this disease affects dogs please visit this page in the PetMD pet health library. Symptoms and TypesRelative Absolute
CausesRelative
Transient
Primary absolute
Secondary absolute
DiagnosisYour veterinarian will perform a complete physical exam on your cat, including a chemical blood profile, a complete blood count, a urinalysis, and an electrolyte panel. Your veterinarian will also measure oxygen levels in the blood. Hormone assays (using blood samples to analyze hormones) can also be used for measuring EPO levels. Radiograph and ultrasound images are also useful for examining the heart, kidneys, and lungs for underlying diseases that could be causing polycythemia. You will need to give a thorough history of your cat's health, including a background history of symptoms, and possible incidents that might have precipitated this condition. The history you provide may give your veterinarian clues as to which organs are causing secondary disease symptoms. TreatmentFor this condition, your cat should be hospitalized. Your veterinarian will decide, dependent on the underlying cause of the polycythemia, whether your cat needs to have some of the excess red blood cells removed by opening a vein - called a phlebotomy, or “letting” - and whether the excess has been caused by low levels of oxygen in the blood, which would require some amount of oxygen therapy. Your cat may also need to be treated with fluid therapy, or with medication if there is a diagnosis of a blood marrow disorder (myeloproliferative/polycythemia vera). Living and ManagementYour veterinarian will schedule follow-up appointments with your pet as necessary to assure a normal packed cell volume, and to follow progress. The primary function of the red blood cells, or erythrocytes, is to carry oxygen from the lungs to body tissues and to transfer carbon dioxide from the tissues to the lungs. Oxygen transfer is accomplished via the hemoglobin contained in red blood cells. Hemoglobin combines readily with oxygen and carbon dioxide. Oxyhemoglobin in arterial blood reflects a bright red color while carboxyhemoglobin of venous blood appears dark red. To enable the maximum O2 saturation of hemoglobin, red cells are shaped like biconcave disks. The shape provides more surface area for exposure of hemoglobin to dissolved oxygen. Red blood cells are also able to change shape to permit passage through small capillaries that connect arteries with veins. The RBC is a count of the number of red blood cells per cubic millimeter of blood. In response to hypoxia, the hormone erthyropoietin, secreted by the kidneys, stimulates the bone marrow to produce red blood cells. The formation of red blood cells is known as erthyropoiesis. Normal red blood cells values at various ages are:
Instant Feedback: Erythropoetin produced in the kidney stimulates the bone marrow to produce more red blood cells. Increase in red blood cells: An increase in red blood cell mass is known as polycythemia. Normal physiological increases in the RBC count occurs at high altitudes or after strenuous physical training. At high altitudes, less atmospheric weight pushes air into the lungs, causing a decrease in the partial pressure of oxygen and hypoxia. With strenuous physical training, increased muscle mass demands more oxygen. The drugs gentamicin and methyldopa have been associated with increasing the number of red blood cells. Smokers also have a higher number of red blood cells than non-smokers. There are also pathological reasons for an increased number of red blood cells. Polycythemia vera is a disease of unknown origin that results in an abnormal increase in red blood cells. Polycythemia vera is referred to as a "primary polycythemia" because the overproduction of red blood cells does not result from hypoxia. The term "vera" means true; thus polycythemia vera refers specifically to overproduction of red blood cells in the bone marrow not caused by a physiologic need. Polycythemia vera is treated by radioactive phosphorus to slow down bone marrow overproduction of red blood cells. Hydration is an important consideration when caring for patients with abnormally high red blood cell counts. Very high RBC mass will slow blood velocity and increase the risk of intravascular clotting. Examples of "secondary polycythemias", that occur in response to hypoxia, are chronic lung disease in adults and children with congenital heart defects characterized by cyanosis. Instant Feedback: Smokers have more red blood cells than non-smokers do. Decrease in red blood cells: A lower than normal RBC can result from a number of causes, including:
The term "anemia" is a general term that refers to a decrease in red blood cells. Anemia can occur from either a decrease in the number of red blood cells, a decrease in the hemoglobin content, or both. Red blood cells live for approximately four months in the bloodstream.  Normal ranges for reticulocytes are 0.5% to 1.5% of the total numbers of red blood cells in men and 0.5% to 2.5% in women. A low reticulocyte count is seen with cirrhosis, folic acid deficiency, and bone marrow failure. A high reticulocyte count indicates that the bone marrow is responding to the need for increased red blood cell production. A person who has recently donated whole blood or who is responding to treatment for anemia would be expected to have a high reticulocyte count. |
