Polycythemia is an abnormally high red blood cell count — the opposite problem of anemia. In cats it is uncommon but important: untreated polycythemia thickens the blood, slows circulation, and risks neurologic and cardiac complications. The cause matters — dehydration, heart disease, kidney tumors, and a rare primary bone marrow disorder can all produce the same blood picture (Cook & Lothrop, 1994, JVIM).
Last reviewed: May 2026
What Polycythemia Means in a Cat
A normal cat's packed cell volume (PCV) — the percentage of blood volume made up of red cells — runs 30 to 45 percent. Polycythemia is defined as PCV above about 55 to 60 percent and is divided into three categories: relative polycythemia (dehydration concentrating normal red cells), secondary appropriate polycythemia (the body makes more red cells in response to chronic low oxygen, often from heart or lung disease), and primary or secondary inappropriate polycythemia (the bone marrow overproduces red cells either on its own or in response to a kidney tumor producing excess erythropoietin).
Signs Owners Notice
Many cats with mild polycythemia have no obvious signs and are diagnosed on routine bloodwork. As PCV rises into the high 60s and 70s, blood becomes thicker (hyperviscosity) and circulation slows. Signs include brick-red or dark purplish gums (often the first thing a vet notices), increased thirst and urination, decreased appetite, weight loss, sluggishness, and intolerance to exercise. Severe hyperviscosity causes neurologic signs — seizures, behavior change, blindness, or sudden collapse — and bleeding tendencies from poor capillary flow.
Causes by Category
Relative polycythemia is the most common and the easiest to treat: dehydration from vomiting, diarrhea, decreased water intake, or diabetes mellitus. Rehydration corrects it within 24 hours. Secondary appropriate polycythemia is the body's normal response to chronic hypoxia — common causes include cardiac disease with right-to-left shunting, chronic respiratory disease such as asthma, and high-altitude living. Inappropriate polycythemia includes renal cyst or tumor producing erythropoietin and the primary form (polycythemia vera), a slow-growing bone marrow disorder seen rarely in older cats.
How Vets Diagnose It
Workup starts with bloodwork (CBC confirming high PCV), urinalysis, biochemistry panel, and an arterial blood gas if available to assess oxygenation. Echocardiography rules out heart disease causing chronic hypoxia. Abdominal ultrasound looks for kidney tumors or cysts. Erythropoietin (EPO) levels — low in primary polycythemia vera, high in renal tumor-driven cases — can be measured at specialty labs. The 2021 AAFP Senior Care Guidelines recommend a thorough workup in any cat over 7 years with unexplained bloodwork abnormalities.
Treatment by Cause
Relative polycythemia from dehydration: IV or subcutaneous fluids, addressing the underlying cause. Secondary appropriate: treat the heart or lung disease — oxygen, bronchodilators, cardiac medications. Lowering the PCV here is not the goal because the high red cell count is compensating for low oxygen. Primary polycythemia or renal tumor: therapeutic phlebotomy (removing 10 to 20 mL of blood per kilogram every 1 to 4 weeks as needed) and sometimes oral hydroxyurea. Surgical removal of a kidney tumor (nephrectomy) is curative if the cat has good function in the other kidney.
When to See a Vet
Call your vet today if:
- Brick-red, dark, or purple-tinged gums in a cat
- Unexplained behavior change in an older cat
- Increased thirst and urination plus reduced appetite
- A cat with known heart or kidney disease who shows new lethargy
- Abnormal red cell count on routine bloodwork
Go to the ER immediately if:
- Sudden seizures, collapse, or inability to walk
- Sudden blindness or severe disorientation
- Bleeding from the gums, nose, or vent without trauma
- Severe rapid breathing with blue or red-purple gums
- Profound weakness in a previously normal cat
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Frequently Asked Questions
How much does workup and treatment cost?
Bloodwork plus urinalysis runs $200 to $400. Echocardiography is $400 to $800. Abdominal ultrasound is $300 to $600. EPO testing at a specialty lab is $100 to $200. Therapeutic phlebotomy in-clinic is $150 to $400 per session and may be needed every 2 to 4 weeks. Hydroxyurea is $30 to $80 per month. Renal tumor surgery is $3,000 to $6,000 at a specialty hospital.
Can polycythemia be cured?
It depends on the cause. Dehydration-driven relative polycythemia resolves with rehydration. Renal tumor-driven cases can be cured with nephrectomy if the tumor is solitary and the other kidney is healthy. Primary polycythemia vera is managed long-term with phlebotomy and oral medication and can have a good quality of life for years. Hypoxia-driven secondary polycythemia depends on whether the underlying heart or lung disease can be controlled.
Is high PCV ever normal?
Mild relative elevation can occur after exercise, stress, or mild dehydration and resolves quickly. A persistently elevated PCV on two samples taken hours to days apart, especially without an obvious cause, warrants workup.
What does brick-red gum color mean exactly?
Healthy cat gums are bubble-gum pink. Brick red or dark purplish-red gums indicate either polycythemia or carbon monoxide exposure. Pale gums indicate anemia or shock. Yellow gums indicate jaundice. Blue or gray gums indicate inadequate oxygen. Gum color is one of the fastest physical-exam clues for several major emergencies.
Will my cat need lifelong treatment?
For dehydration-driven polycythemia, no — once the underlying cause is fixed, the problem resolves. For polycythemia vera, yes — periodic phlebotomy is needed for life. For secondary polycythemia from heart or lung disease, treatment of the underlying condition is lifelong, but specific polycythemia treatment usually is not.
Still Not Sure if Your Cat Needs a Vet?
When you're not sure if this is wait-and-see or call-tonight, Voyage AI Vet triages in under 2 minutes. Describe what you're seeing in chat, share photos of your cat's gum color (a dark red or purplish tint is significant) and any disorientation, or hop on a live video call if you want a second pair of eyes. Every answer comes with citations to the actual veterinary literature it's pulling from — so you see exactly where the guidance comes from, not just a chatbot's word.