🩸 Vet-Approved Guide to Immune-Mediated Hemolytic Anemia (IMHA) in Pets (2025) 🐶🐱

By Dr Duncan Houston BVSc

Immune-Mediated Hemolytic Anemia (IMHA) is one of the most severe autoimmune conditions affecting dogs and cats 🧬. It occurs when the immune system mistakenly attacks and destroys red blood cells, leading to severe anemia, organ strain, and potentially fatal blood clots. In this comprehensive 2025 veterinary guide, Dr Duncan Houston explains how to recognize, diagnose, and treat IMHA with urgency and precision 🏥⚠️.

🔍 What Is IMHA?

Immune-Mediated Hemolytic Anemia (IMHA)—previously known as Autoimmune Hemolytic Anemia (AIHA)—is a condition in which the body identifies its own red blood cells as threats and destroys them 🧫. This creates:

• 💉 Severe anemia (low red blood cell count)
• 🟡 Jaundice (yellow tissues and urine)
• 🧱 Dangerous blood clots (thromboembolism)
• 🫁 Poor oxygen delivery to organs

The mortality rate can range from 20% to 80% depending on how early and aggressively the condition is treated.

🩺 How Red Blood Cells Are Normally Removed

Healthy red blood cells circulate for about 3 months before being broken down in the liver, spleen, or bone marrow. Their components—iron, protein, and waste—are recycled efficiently 🧪. In IMHA, the immune system marks healthy red cells for destruction prematurely, causing a catastrophic loss of oxygen-carrying capacity and a dangerous buildup of byproducts like bilirubin and hemoglobin 🧬.

⚠️ What Happens During IMHA?

During IMHA, the body initiates an autoimmune cascade:

• 🧫 Red blood cells become coated in antibodies
• 🟠 Bilirubin builds up, turning tissues yellow (jaundice)
• 🧪 Hemoglobin is released and may damage kidneys
• 🧱 Antibody-coated cells clump and block vessels (thromboembolism)

This cascade creates multi-organ stress, poor circulation, and, in some cases, death. Aggressive treatment is the only path to survival 🆘.

🧾 Clinical Signs and Diagnosis

🐾 Signs to Watch For:

• 😴 Lethargy and weakness
• 🐽 Pale or yellow gums
• 🍊 Dark orange or brown urine
• 🌡️ Fever or loss of appetite

🔬 Key Diagnostic Clues:

• 🧪 High bilirubin and orange urine
• 🔍 Spherocytes on blood smear
• 🩸 Positive Coombs test (detects immune-coated red cells)
• 🧬 Autoagglutination (clumping of red cells on slide)
• 📉 Elevated lactate (indicates poor oxygen delivery)

Veterinarians will also rule out other causes of anemia, like tick-borne parasites (Ehrlichia, Babesia), toxins (zinc, onions), or blood loss.

🩹 Treatment Strategies

IMHA treatment must be urgent and aggressive. The top priorities are:

• 🔴 Suppress the immune system
• 🩸 Restore red blood cell levels with transfusions
• 🛡️ Prevent deadly blood clots

1. 💉 Blood Transfusions

Used to restore oxygen levels quickly. Some pets may need multiple transfusions as their body continues to destroy both their own and donated red cells.

2. 💊 Immune Suppression

• Prednisone/Dexamethasone: cornerstone treatment to stop red cell destruction
• Azathioprine: used if steroids alone aren't effective
• Cyclosporine: expensive but effective alternative for severe cases
• Mycophenolate Mofetil: another emerging immune suppressant

These medications can have side effects and must be monitored through bloodwork. Most pets are on medication for 4 months or longer 🗓️.

3. 🧬 Preventing Clots

Thromboembolic disease is the leading cause of death in IMHA patients. Prevention options include:

• 💉 Low-dose Heparin
• 💊 Clopidogrel (Plavix®)
• 💊 Ultra-low dose Aspirin

Each option has risks, especially in pets with platelet issues (like Evans syndrome), so medications are selected carefully 🔎.

🧪 Monitoring & Hospitalization

• 💉 Frequent hematocrit checks
• 🩺 Monitor clotting, lactate levels, and organ function
• 🏥 Most pets stay in ICU for 4–6 days

📊 Prognosis

• 📉 Mortality rate: 20–80%
• 📆 Average hospital stay: 4–6 days
• 🔁 Relapse rate: 11–15%

Survival improves with early diagnosis, aggressive care, and clot prevention.

🐶 Breed & Risk Factors

Breeds predisposed to IMHA include:

• Cocker Spaniels
• Poodles
• Old English Sheepdogs
• Irish Setters

Unspayed females and neutered males are statistically more at risk. In cats, IMHA is often linked to feline leukemia virus (FeLV) or Mycoplasma haemofelis.

📌 Evans Syndrome

Evans syndrome is when the body destroys red cells and platelets at the same time 🧨. These pets are at increased risk for bleeding, and traditional clot-prevention may worsen bleeding risk. Mortality is higher.

🧠 Why Did IMHA Happen?

Often, no trigger is found. But potential causes include:

• 💊 Drug reactions
• 🧬 Tick-borne disease or parasites
• 🦠 Cancer (e.g., hemangiosarcoma)
• 💉 Possibly vaccines (controversial)

📲 Final Advice from Dr Duncan Houston

IMHA is one of the most urgent diseases in veterinary medicine. If your pet shows yellow eyes, pale gums, brown urine, or extreme weakness—seek emergency care right away ⚠️. Early, aggressive therapy gives your pet the best chance of survival.

Download the Ask A Vet App or visit AskAVet.com to access emergency guidance, medication advice, and connect with licensed professionals 24/7 🐾🆘.