Polycythemia in Dogs

Polycythemia is a condition that is characterized by a thickening of the blood, either due to a shortage of the amount of plasma in the blood or due to an increased number of red blood cells in circulation. This condition can prevent blood from getting through smaller blood vessels which prevent oxygen from reaching the tissues fed by those vessels. There are several categories of polycythemia, usually differentiated by their underlying cause and the duration of the disorder.

Polycythemia is a condition in which the blood becomes thicker than normal, and the ratio of plasma cells to red blood cells becomes unbalanced.

Polycythemia is characterized by a thickening of the blood which impedes the passage of blood through the smaller blood vessels, causing a lack of oxygen to the area that vessel feeds. This can be especially problematic when the brain or kidneys are involved. Possible symptoms could include:

• Abnormal behavior
• Difficulty breathing
• Enlarged liver
• Enlarged spleen
• Exhaustion
• Increased thirst
• Increased urination
• Lack of coordination
• Lethargy
• Nose bleeds
• Pale or brick red gums
• Seizures 
• Sudden violent and recurring sneezing
• Weakness

Types

• Absolute - This is an actual increase in the production of red blood cells, possibly due to a primary process in the bone marrow itself; there is both a primary and secondary subtype of absolute polycythemia
• Relative - In this type of polycythemia, the thickening of the blood is caused by a reduction in the volume of liquid plasma in the blood rather than an increase in red blood cells; vomiting or diarrhea can cause dehydration, leading to a relative polycythemia
• Transient - This polycythemia is a temporary condition due to a contraction of the spleen, which releases additional red blood cells into the bloodstream; this contraction of the spleen is usually due to a release of adrenaline due to excitement or fear

Relative polycythemia is caused by depletion of the plasma volume in the blood. This can be due to a number of reasons, including disorders like dehydration, blood loss, kidney disease, or parasites.

Transient polycythemia is caused by an increase in adrenaline due to excitement or fear and is usually harmless and short-lived.

Secondary absolute polycythemia is generally caused by a disorder of the kidneys that stimulates the bone marrow to create more red blood cells due to an overproduction of the hormone erythropoietin. Primary absolute polycythemia occurs when the actual bone marrow tissue increases, causing more red blood cells to be circulated. The source of the tissue growth that causes primary absolute polycythemia is unknown as it is rare.

A thorough history and physical exam will be completed by your veterinarian when you visit the clinic, and standard tests, including a urinalysis, blood chemistry profile, and a complete blood count will be evaluated. Not only will these tests uncover the oversaturated blood, but they will also assist in identifying the type of polycythemia that is afflicting the patient. Tests will be run to check the plasma and protein concentrations as well as the oxygen levels in the blood.

Imaging technologies such as x-ray and ultrasound may also be used to more clearly visualize the heart and lungs, in order to identify any underlying conditions that may be causing the coagulation of the blood. Electrocardiographs (ECGs) can be used to evaluate the other internal organs by detecting blood clots in the lungs or heart abnormalities that may not be apparent from x-ray imaging, and also to measure the blood vessels during heart contraction.

Dogs with transient polycythemia rarely develop any complications and the condition usually reverses itself quickly so treatment may not be required. General supportive therapies for canines in distress could include treatments such as IV fluid therapy to prevent additional dehydration and to improve blood pressure, medications to dilate the bronchial tubes and oxygen supplementation. With both relative and secondary absolute polycythemia, the underlying cause must be addressed before the disorder can be reversed. Quite often fluid therapy is enough to normalize the consistency of the blood in the case of relative polycythemia.

Absolute polycythemia usually requires additional treatment methods. Secondary absolute polycythemia is often triggered by hypoxia, a lack of oxygen to the body tissues. The deficiency of oxygen can be caused by conditions as diverse as an adjustment to high altitudes, hyperthyroidism, or cancer. The reduced oxygen levels prompt the kidneys to increase their production of the hormone erythropoietin, a hormone that stimulates the bone marrow to increase production of red blood cells.

Many dogs with transient or mild relative polycythemia never show symptoms and recover spontaneously. Even with more challenging cases, once the appropriate treatments or management techniques are implemented to address the underlying condition most dogs with polycythemia recover completely and often fairly quickly. Canine compulsive disorder is a condition that occurs in dogs that are remarkably similar to obsessive-compulsive disorder in humans. Studies have indicated that there is a connection between dogs with compulsive disorders and somewhat increased red blood cell concentrations. Approximately one-quarter of the dogs in one of the studies with compulsive disorder dogs had levels of red blood cells that were sufficient to cause polycythemia.