What is erythrocytosis in dogs and cats?

Erythrocytosis refers to an abnormally high number or concentration of red blood cells in the blood. It may be relative (due to dehydration) or absolute (due to increased production), and requires veterinary investigation to determine the cause.

What tests will the vet run to find the cause?

Common investigations include a complete blood count, blood biochemistry, coagulation profile, chest and abdominal imaging, and — when necessary — bone marrow examination or advanced imaging to determine the cause and severity.

What can I observe or prepare at home?

Record when symptoms began, track daily food and water intake and activity levels, take short videos of breathing or alertness, and bring any past test reports for your vet's reference.

How often does erythrocytosis need to be monitored?

Monitoring frequency depends on the underlying cause and treatment response; blood count and biochemistry checks may be needed weekly to monthly. Follow your vet's recommended schedule.

How much do the tests and treatment usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Erythrocytosis in Dogs & Cats: Symptoms, Diagnosis & Home Care Guide [2025]

Erythrocytosis is a condition in which red blood cell counts are abnormally elevated. It may be primary or secondary to cardiopulmonary disease, tumours, or other causes. It can increase the risk of blood-related complications; treatment includes phlebotomy and addressing the underlying cause.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: ACVIM, AVMA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek Emergency Care Immediately

•Heavy external bleeding that cannot be stopped requires immediate attention
•Continuous seizures or repeated brief loss of consciousness
•Obvious difficulty breathing with color changes in the lips or mucous membranes

Schedule a Clinic Visit Soon (within 24–72 hours)

•Noticeably and persistently lower energy and vitality than usual
•Reduced appetite or short-term refusal to eat without recovery
•Repeated minor external bleeding or intermittent nosebleeds

01What symptoms indicate something is wrong?

Erythrocytosis in dogs and cats often presents with non-specific systemic symptoms. In severe cases, increased blood viscosity or platelet dysfunction may lead to bleeding, neurological signs, or respiratory changes.

Lethargy, drowsiness, or a noticeable drop in activity level
Reduced appetite or a significant decrease in food intake over a short period
Reduced water intake or signs of dehydration (decreased skin elasticity)
Recurrent nosebleeds or minor external bleeding
Seizures, behavioural changes, or brief episodes of altered consciousness

Seek emergency care immediately if you notice the following symptoms:

⚠️ Profuse external bleeding that cannot be stopped requires immediate attention
⚠️ Continuous seizures or repeated brief episodes of loss of consciousness
⚠️ Obvious breathing difficulty with a change in gum or mucous membrane colour

02How to assess abnormalities at home: observation tips and emergency criteria

Recording key information at home helps your vet quickly understand the timeline of symptoms and improves the efficiency of diagnosis and treatment.

Note the exact date and time when symptoms first appeared
Record daily food intake, water consumption, and changes in activity level
Use your phone to video your pet's alertness and breathing
Observe and record urine colour, frequency, and bowel movements
Weigh your pet at a consistent time and note any weight trend
Bring all notes and videos to the vet appointment

03How will the vet diagnose the problem? Common diagnostic tests

At the clinic, blood tests and imaging are the primary tools; further investigations may be needed to clarify the underlying cause and severity.

Physical examination

assessment of mucous membrane colour, pulse, and temperature

Blood tests

complete blood count (RBC, HCT, HGB)

Blood biochemistry and coagulation profile to assess organ function and bleeding risk

Chest and abdominal X-rays or ultrasound to assess organ changes

Advanced imaging (CT) or bone marrow examination to identify the underlying cause

04What treatment and care are needed after diagnosis? Medications, dietary adjustments, and care guide

Treatment is tailored to the underlying cause and may include medication, phlebotomy, and supportive care, with regular monitoring of blood counts and clinical response.

The primary goal is to manage the underlying cause of erythrocytosis
Immune-mediated or oncological treatments may be needed depending on the vet's assessment
Supplemental oxygen and other supportive care can temporarily relieve respiratory symptoms
Home care includes dietary adjustments, ensuring adequate hydration, and rest management
Regular follow-up visits to monitor blood cell counts and organ biochemistry markers
Long-term follow-up is recommended at a clinic with specialist diagnostic capabilities

05What to prepare before the vet visit: key information to help your vet quickly identify the cause

Bring a symptom log (onset time, progression) for the vet to review

Record and note daily food intake, water consumption, and weight changes

Prepare records of bowel and bladder habits and photos or videos of any bleeding

List all current and recent medications and supplements

Bring any previous blood test results, imaging reports, or medical records if available

Transport your pet in a secure carrier and book an appointment at a clinic that can perform blood tests

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.