Polycythemia in Cats

Angela Beal, DVM, FFCP
By Angela Beal, DVM, FFCP on Feb. 27, 2024
A cat is examined by their veterinarian.

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In This Article


What Is Polycythemia in Cats?

Polycythemia in cats is a rare condition that is characterized by an abnormally high number of red blood cells (RBCs). This thickens the blood, making it more difficult to flow easily through smaller veins and capillaries. Inadequate blood flow leads to poor oxygen delivery to tissues and can result in severe circulatory problems, including heart failure.

The brain and muscles require the most nutrients and oxygen. When polycythemia inhibits blood flow to these organs, cats can experience lethargy, weakness, and potentially seizures.

If left untreated, polycythemia can damage the heart. Polycythemia is a serious condition that can be fatal. If you notice symptoms of polycythemia in your cat, bring them to the veterinarian immediately.

Types of Polycythemia in Cats

Types of polycythemias in cats include:

  • Absolute—Absolute polycythemia can be further classified as:

    • Primary—Primary polycythemia, also known as polycythemia rubra vera, causes uncontrolled RBC production by the bone marrow. White blood cells (WBCs) and platelets may also be elevated. Often, an affected cat’s packed cell volume (PCV), the percentage of the blood composed of RBCs, is 65% or higher. Cats with primary polycythemia have been reported to live five years or more.

    • Secondary—Erythropoietin is a hormone produced by the kidneys that signals the bone marrow to produce more RBCs. Secondary polycythemia is caused by conditions that increase erythropoietin production. Examples include heart disease, chronic respiratory problems, kidney disease, and hyperthyroidism. The prognosis for cats with secondary polycythemia depends on the underlying cause.

  • Relative—Relative polycythemia refers to an increase in PCV secondary to dehydration. Because the blood contains less water, the cells compose a greater percentage of the overall volume. This rarely results in a PCV greater than 60% in cats.

  • Transient—Transient (short-lived) polycythemia is caused by contraction of the spleen, resulting from excitement or stress, which releases RBCs into the bloodstream. This type of RBC elevation is not long-term.

Symptoms of Polycythemia in Cats

Symptoms of polycythemia in cats can include:

Causes of Polycythemia in Cats

Polycythemia in cats is a rare condition, and no breed, age, or gender is identified as being at higher risk. One cause, polycythemia rubra vera, is a bone marrow disorder that results in RBC overproduction.

Other causes of polycythemia include:

  • Dehydration—Dehydration is the most common cause, as it leads to an increase of RBCs in proportion to fluid in the blood. Dehydration can be caused by vomiting, diarrhea, or decreased water intake.

  • Stress—Stress can cause the spleen to contract, resulting in transient polycythemia.

  • Conditions that inhibit blood flow—When a cat has a condition (such as obesity, chronic heart or lung disease, cancer, hormonal disease, or kidney disease) that inhibits oxygen delivery to the tissues, their body may compensate by producing additional RBCs to keep up with oxygen demand.

How Veterinarians Diagnose Polycythemia in Cats

Diagnosis of polycythemia in cats involves not only determining if your cat has an increased RBC level but also diagnosing the underlying cause. Diagnostics may include:

  • Complete blood count (CBC)—A CBC evaluates your cat’s RBCs, WBCs, and platelets to assess the cells’ size and determine if levels are appropriate.

  • Total protein—If your cat’s total protein is also elevated, dehydration is likely causing the polycythemia.

  • Biochemistry—A biochemistry profile can help your veterinarian determine if your cat has an underlying condition causing the polycythemia.

  • Oxygen saturation—Oxygen saturation measures the amount of oxygen in the blood. If your cat’s oxygen saturation is low, your veterinarian will perform further diagnostics to identify what could be causing the issue.

  • Erythropoietin—If erythropoietin levels are elevated, your cat is likely affected by an issue, such as heart or lung disease, cancer, or a hormonal disease, which triggers excessive erythropoietin production.

  • Imaging—Imaging, such as X-rays and/or ultrasound, may be needed to rule out underlying issues.

  • Bone marrow biopsy—A bone marrow biopsy can provide more information to facilitate a polycythemia diagnosis.

  • Heart evaluation—Because polycythemia can affect your cat’s heart, your veterinarian may recommend a cardiac workup that includes an electrocardiogram (EKG) and an echocardiogram.

Treatment of Polycythemia in Cats

Treatment of polycythemia in cats depends on the condition’s underlying cause and may include:

  • Intravenous (IV) fluids—If dehydration is the cause of your cat’s polycythemia, IV fluids will be administered to rehydrate them.

  • Oxygen therapy—Your cat may need oxygen therapy if their blood oxygen saturation is low.

  • Phlebotomy—Phlebotomy involves placing an IV catheter, removing a certain volume of blood, and replacing the blood with IV fluids to dilute the blood cell concentration.

  • Hydroxyurea—Hydroxyurea is a chemotherapy drug that works by slowing the bone marrow’s production of RBCs. RBCs live about 120 days, so positive effects won’t be observed for a while. Potential hydroxyurea side effects include vomiting, diarrhea, and lack of appetite.

Recovery and Management of Polycythemia in Cats

During recovery, your cat must get plenty of rest and be kept quiet.

Your veterinarian will likely recommend rechecking your cat’s bloodwork once a week for the first month, monthly for the next three months, and every three months thereafter to check the bone marrow’s response to treatment.

Some pets can be weaned off hydroxyurea after a year or two, but others must remain on medication for life.

Prevention of Polycythemia in Cats

There are no known measures to prevent primary polycythemia in cats. However, you can reduce your cat’s risk for other forms of polycythemia by:

Polycythemia in Cats FAQs

How long can a cat live with polycythemia?

With proper monitoring and treatment, most cats can live with polycythemia for many years. Survival times exceeding five years have been reported.

Angela Beal, DVM, FFCP


Angela Beal, DVM, FFCP


Angela Beal is a veterinarian in Columbus, Ohio, who loves helping pet owners provide the best possible care for their beloved companions....

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