Polycythemia in Dogs

What Is Polycythemia in Dogs?

Blood is made up of red blood cells (RBC), white blood cells (WBC), platelets, and plasma (the liquid part). On average, the percentage of the RBC in blood is 35 to 55%. This is known as PCV, or packed cell volume.

Polycythemia, erythrocytosis, and high red blood cell count are all used to describe the increase in RBC either in quantity, hemoglobin (protein that carries oxygen), or PCV.

This increase in red blood cells causes them to collect on the walls of red blood vessels, also called sludging. This causes vessel damage, clot formation, and poor circulation. It also causes decreased blood flow to vital places like the brain, which leads to less oxygen and nutrients. When the brain doesn’t get enough oxygen, symptoms such as seizures and blindness in dogs can occur.

Polycythemia in dogs is a very rare condition with only a few cases reported, and it often develops slowly. Some dogs are diagnosed after routine blood work and before the development of symptoms, and some dogs can remain asymptomatic for years.

Types of Polycythemias in Dogs

Spurious or relative polycythemia occurs when there is normal RBC mass but an increase in the PCV, often in cases of:

• Dehydration

• Strenuous exercise, excitement, or stress

• Severe pain

• Water deprivation

• Heatstroke

• Burns

• Excessive vomiting and diarrhea

Absolute polycythemia occurs when there is an increase in the production of RBC and can be further classified as either:

• Primary, known as polycythemia vera, which occurs when there is cancer of the bone marrow.

• Secondary, which can occur during several conditions such as:

  • Anemia (low red blood cell count)

  • Low atmospheric oxygen (high altitude)

  • Heart dysfunction, congenital heart defects, and clots

  • Carbon monoxide poisoning

  • Respiratory disease

  • Kidney cancer and disease

Symptoms of Polycythemia in Dogs

Symptoms of polycythemia in dogs are typically noticed when the PCV becomes greater than 65%. Signs can include:

• Lethargy and exercise intolerance

• Weakness

• Bright red gums

• Dehydration

• Bloodshot eyes

• Heart murmur

• Respiratory distress

• Increased thirst and urination

• Reddened skin

• Bleeding, which may show as bloody stool, black tarry stool (melena), vomiting blood, or nose bleeds

• Neurologic signs such as behavior changes, seizures, blindness, tremors, or lack of coordination

Causes of Polycythemia in Dogs

Polycythemia in dogs has several causes, depending on the type.

Polycythemia tends to occur more in middle-aged female dogs. Certain breeds, like Greyhounds, normally have high RBC concentrations to begin with, but this isn’t considered abnormal in the breed.

How Veterinarians Diagnose Polycythemia in Dogs

Your vet will want a thorough history of your pet. Then they’ll perform a physical examination with bloodwork and a urinalysis to look for a high PCV, Hgb, and RBC count.

Polycythemia in dogs is a diagnosis of exclusion, meaning that your veterinarian must rule out all other causes first. Additional blood tests, X-rays of the chest and abdomen, echocardiogram of the heart, serum EPO levels, and even a bone marrow aspirate may be recommended.

Treatment of Polycythemia in Dogs

Treatment of polycythemia in dogs varies and often depends on the underlying cause. For example, dogs with relative polycythemia need fluid therapy, and dogs with cancer would need surgery, radiation, chemotherapy, or a combination of treatments.

For many dogs, however, the usual treatment involves phlebotomy, or bloodletting. Thinning the blood allows for easier passage of nutrients and oxygen through vessels to the tissues.

Dogs undergoing treatment often need a several-hour hospital stay. While there, blood is drawn and replaced with IV fluids, which helps dilute the blood.

This procedure may be needed several times over the first few days to get a better PCV (usually less than 55%) so symptoms will clear up.

Polycythemia in dogs can be managed easily for months to years. However, complications such as blood clots can occur. This can result in acute lameness, cold limbs, respiratory distress, or sudden death.

For advanced cases or when significant symptoms are present, humane euthanasia may be recommended.

Recovery and Management of Polycythemia in Dogs

Most dogs will have polycythemia for life and need blood draws every couple of weeks.

Your vet will want to watch the bloodwork more often than that at first, but it will be less often over time. Drawing blood regularly may result in iron deficiency, and you may need to give your dog a supplement.

For dogs needing more frequent phlebotomies, your veterinarian may prescribe additional treatment such as radioactive phosphorous or hydroxyurea, a chemotherapeutic drug that targets the bone marrow, which in turn decreases the production of RBC.

Some dogs may be weaned off the medication over time, but the majority will need it for life. Side effects of this medication when used long-term can include gastrointestinal upset, skin lesions, toenail loss, and bone marrow suppression (when not enough blood cells are produced by the bone marrow).

Speak with your vet about all available therapy options, and what monitoring schedule is best for your pup.

Prevention of Polycythemia in Dogs

Polycythemia in dogs is often unpredictable and not every cause can be entirely prevented. However, there are some measures you can take to help your pup. Water fountains or ice cubes are easy ways to encourage your dog to drink.

Keep your dog hydrated! If too much fluid is lost when they are vomiting or have diarrhea, seek veterinary attention right away.

Don’t leave your dog outside unattended, especially in the summer months, and never leave them in a car.  Only a few minutes in the heat can be fatal.