What is hyperviscosity syndrome?

Hyperviscosity means the blood has become thicker, increasing resistance to blood flow. It may cause low energy, breathing changes, and circulation problems. A vet needs to investigate the cause and treatment options using blood tests and imaging.

What tests will a vet use to diagnose it?

Common tests include a complete blood count, biochemistry profile, urinalysis, and chest or abdominal imaging. Specialised blood testing or tissue sampling may be recommended when needed to identify the cause.

When does this need emergency care?

Seek veterinary care immediately if your pet has obvious breathing difficulty, suddenly collapses, or has heavy ongoing bleeding. Delays can be life-threatening, so contact the nearest veterinary hospital right away.

What is usually needed for follow-up monitoring?

Follow-up usually involves repeat blood tests and biochemistry checks as advised by your vet. Imaging or specialist reassessment may be arranged when needed to confirm treatment response and adjust the treatment plan.

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

Hyperviscosity Syndrome in Dogs and Cats: Symptoms, Diagnosis & Care [2025]

Hyperviscosity syndrome is caused by excessively high immunoglobulin levels in the blood and is commonly associated with multiple myeloma. It can lead to bleeding, neurological signs, and vision problems. Plasmapheresis can provide rapid symptom relief.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

PetHealthMap Editorial Team

Sources: ACVIM, WSAVA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek emergency care immediately

•Obvious difficulty breathing or unable to lie down and rest
•Sudden change in consciousness or brief episode of collapse
•Heavy bleeding from the mouth or nose, or persistent gum bleeding

Schedule a clinic visit soon (within 24–72 hours)

•Noticeably faster breathing and easy fatigue after exercise
•Decreased alertness, sluggish response, or excessive sleepiness
•Significantly increased water intake or change in urination frequency

01What symptoms may indicate a problem?

Excessively high blood viscosity can affect blood flow throughout the body. Common signs include changes in alertness, eating and drinking patterns, and heart or lung function.

Reduced alertness, slower responses, or unusual sleepiness
Poor appetite or a clear drop in food intake
Increased drinking and changes in urination frequency or volume
Worsening panting during activity or laboured breathing at rest
Noticeably faster heart rate and reduced exercise tolerance
Changes in gum colour (pale or darker than usual) or a tendency to bleed

Seek emergency care immediately if you notice the following symptoms:

⚠️ Difficulty breathing or panting so heavily your pet cannot rest
⚠️ Sudden change in consciousness or a brief collapse
⚠️ Heavy bleeding or gum bleeding that does not stop

02How can you assess changes at home? Key observations and emergency warning signs

Observing and recording symptom details and timing at home helps your vet assess severity and decide which tests are most appropriate.

Record when signs started, how long they last, and how they change
Measure and write down daily water intake and urination frequency and volume
Observe appetite, food regurgitation or vomiting, and any complete refusal to eat
Take short videos of breathing at rest and during activity
Watch for changes in gum colour or any unexplained signs of bleeding
Bring these notes and videos to the vet appointment for reference

03How will a vet make the diagnosis? Common tests

At the clinic, diagnosis usually starts with a physical examination and laboratory tests. Imaging and specialised tests may be added when needed to identify the underlying cause.

Physical examination

listening to the heart and lungs, checking mucous membrane (gum) colour and capillary refill time

Blood tests

a complete blood count and assessment of red blood cells and blood-viscosity-related indicators

Biochemistry tests

assessment of liver, kidney, electrolyte, and metabolic abnormalities

Urinalysis

to rule out urinary tract infection or kidney function problems

Diagnostic imaging

chest and abdominal X-rays or heart/abdominal ultrasound to assess organ changes

Advanced testing

CT or tissue biopsy (histopathology) may be recommended when needed to clarify the underlying cause

Further assessment and discussion at a hospital with cardiology or internal medicine specialists may be recommended

04How is it treated and managed after diagnosis? Medication, diet changes, and care guidance

Treatment focuses on stabilising blood flow and managing the underlying cause. Regular follow-up tests and imaging should be performed as advised by your vet to assess response to treatment.

Short-term supportive care aims to stabilise vital signs and improve blood flow
Further treatment is decided after a specialist clarifies the underlying cause
Follow your vet's schedule for repeat blood tests, biochemistry, and imaging to monitor changes
Adjust diet and home care according to your vet's recommendations
Regular imaging or tissue follow-up may be arranged when needed to assess treatment response
Long-term follow-up at a hospital with cardiology or internal medicine specialists is recommended

05What should you prepare before seeing the vet? Key details that help identify the cause

Write down when symptoms started and detailed notes on daily changes

Record water intake and urination frequency and volume over the past few days

Note food type, appetite changes, and any vomiting

List all current medications, supplements, and dosages

Take short videos showing breathing and activity levels at rest and during movement

If possible, book an appointment with a cardiology or internal medicine specialist clinic in advance

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.