Polycythemia in Dogs
Polycythemia is a serious blood disorder marked by an abnormal increase in the quantity of red blood cells within the circulatory system. It involves elevated levels of packed cell volume (PCV), hemoglobin concentration (the red pigment in blood cells), and red blood cell (RBC) count, exceeding standard reference intervals due to either a relative, transient, or absolute rise in circulating red blood cells.
There are three classifications of polycythemia: relative, transient, and absolute. Relative polycythemia occurs when a reduction in plasma volume, often due to dehydration, leads to a relative increase in circulating RBCs. Transient polycythemia results from splenic contraction, which releases concentrated RBCs into circulation momentarily in response to epinephrine, the hormone triggered by stress, anger, and fear. Absolute polycythemia entails a definite increase in circulating RBC mass, typically due to heightened bone marrow production.
Absolute polycythemia, characterized by increased RBC production in the bone marrow, can be either primary or secondary to elevated levels of EPO. Primary absolute polycythemia, known as polycythemia rubra vera, is a myeloproliferative disorder marked by uncontrolled overproduction of RBCs in the bone marrow. Secondary absolute polycythemia results from a physiologically appropriate release of EPO caused by chronic hypoxemia (oxygen deficiency) or from inappropriate and excessive production of EPO or EPO-like substances in an animal with normal blood oxygen levels.
This condition affects both dogs and cats.
Symptoms and Types
Relative:
- Vomiting
- Diarrhea
- Reduced water intake
- Increased urination
Absolute:
- Fatigue
- Reduced tolerance for exercise
- Gums appearing dark-red or bluish
- Sneezing
- Nosebleeds
- Enlarged abdomen
Causes
Causes
Relative:
- Vomiting
- Diarrhea
- Decreased water intake
- Kidney disease
- Hyperventilation
Transient:
- Excitement
- Anxiety
- Seizures
- Restraint
Primary absolute:
- Rare myeloproliferative disorder (bone marrow disorder)
Secondary absolute:
- Hypoxemia (insufficient oxygen in the blood)
- Chronic lung disease
- Heart disease
- High altitude
- Impaired blood supply to the kidneys
- Inappropriate EPO secretion
- Kidney cyst
- Kidney swelling due to urine backup
- Overactive adrenal gland
- Overactive thyroid gland
- Adrenal gland tumor
- Cancer
Diagnosis
Your veterinarian will conduct a comprehensive physical examination of your dog, which includes a chemical blood profile, a complete blood count, a urinalysis, and an electrolyte panel. Oxygen levels in the blood will also be measured. Hormone assays using blood samples can aid in assessing EPO levels. Radiographs and ultrasound images will be utilized to examine the heart, kidneys, and lungs for any underlying diseases contributing to polycythemia.
Providing a detailed history of your dog’s health, including symptoms and potential triggering incidents, is crucial. This history can offer valuable insights to your veterinarian regarding which organs may be implicated in secondary disease symptoms.
Treatment
For this condition, your dog will require hospitalization. Depending on the underlying cause of polycythemia, your veterinarian will determine if your dog needs to undergo phlebotomy, which involves removing some of the excess red blood cells by opening a vein, or “letting”. Oxygen therapy may be necessary if the excess red blood cells are due to low blood oxygen levels. Fluid therapy may also be administered, and medication may be prescribed if there is a diagnosis of a bone marrow disorder such as myeloproliferative/polycythemia vera.
Recovery and Management
Your veterinarian will arrange follow-up appointments with your dog as needed to ensure a normal packed cell volume and to monitor progress.