Overproduction of Red Blood Cells in Dogs

By PetMD Editorial on Nov. 4, 2008

Polycythemia in Dogs

Polycythemia is a rather serious blood condition, characterized as an abnormal increase in the amount of red blood cells in the circulatory system. 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.

The condition affects both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

Relative

Vomiting
Diarrhea
Lack of water intake
Excessive urination

Absolute

Lack of energy
Low exercise tolerance
Dark-red, or bluish gums
Sneezing
Nosebleeds
Enlarged abdomen

Causes

Relative

Vomiting
Diarrhea
Diminished water intake
Kidney disease
Hyperventilation

Transient

Excitement
Anxiety
Seizures
Restraint

Primary absolute

Rare myeloproliferative disorder(bone marrow disorder)

Secondary absolute

Not enough oxygen in the blood (hypoxemia)
- Long-term lung disease
- Heart disease
- High altitude
- Impairment of blood supply to the kidneys
Inappropriate EPO secretion
- Kidney cyst
- Swelling of a kidney due to urine being backed-up
- Overactive adrenal gland
- Overactive thyroid gland
- Tumor of the adrenal gland
- Cancer

Diagnosis

Your veterinarian will perform a complete physical exam on your dog, 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 dog'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.

Treatment

For this condition, your dog should be hospitalized. Your veterinarian will decide, dependent on the underlying cause of the polycythemia, whether your dog 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 dog 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).