Immune-Mediated Hemolytic Anemia (IMHA) in Dogs

Red blood cells are important because they contain hemoglobin, which carries oxygen to the body’s tissues.  The reduction of red blood cells caused by IMHA directly affects how much oxygen the tissues are receiving. Without the proper amount of oxygen, the body’s organs cannot function normally. 

The destroyed red blood cells result in a buildup of hemoglobin, which the liver attempts to “clean” by producing more bilirubin.  The excess bilirubin causes patients with IMHA to appear jaundiced.

All breeds can have immune-mediated hemolytic anemia but there are more documented cases in Cocker Spaniels, Labrador Retrievers, Poodles, Irish Setters, Shih Tzu, and Old English Sheepdogs.  Young to middle age females are more predisposed. 

If your dog is showing symptoms of IMHA he should be seen by a veterinarian as soon as possible.  Immune-mediated hemolytic anemia can be fatal if not treated.

Immune-mediated hemolytic anemia in dogs is a disease where the immune system attacks and breaks down the body’s red blood cells.  The immune system normally defends the body from bacteria and virus infections.  The disease causes abnormal antibodies to fend off the body’s own red blood cells.  The red blood cells are destroyed faster than the bone marrow is manufacturing them.

• Lethargic
• Tachycardia - Fast heart beat
• Polyuria - Frequent urination
• Darker colored urine
• Tarry/dark stool 
• Polydipsia - Increased thirst
• Pallor - Paleness seen on the gums, underside of the ears and the inner eyelids
• Jaundice (icterus) - Yellow pigmentation in the sclera (white part of the eye), along the gum line, pinnae (inner ear flap), genitals and on the abdomen
• Weakness
• Decreased ability to exercise
• Dyspnea - Shortness of breath
• Lack of appetite 
• Fainting
• Nose bleeds
• Seizures
• Vomiting
• Collapse

Types

• Primary IMHA (idiopathic) - No underlying reason for the disease (this is the most common type of IMHA; 60-75% of patients with immune-mediated hemolytic have primary IMHA)
• Secondary IMHA - Is triggered by a condition or activated by an agent

Primary IMHA 

• The body’s own immune system is at fault. 
• Genetic implications

Secondary IMHA 

IMHA can be triggered by:

• Recent vaccination 
• Medications
• Tick exposure
• Zinc or copper intoxication ( ingesting pennies, batteries, zinc oxide cream)
• Cancer
• Toxins
• Stress of estrus 
• Infections caused by Babesia, Ehrlichia, and Leishmania

If your pet has been seen by another veterinarian it is recommended that you bring his medical records with you. Even if it was just a wellness check, the records can provide a baseline.  The veterinarian will go over the patient’s medical history.  Let the veterinarian know if your pet is on any current medications, has had recent vaccinations or has been exposed to any toxins.

The veterinarian will perform a physical examination on the patient.  The examination may include taking the patient’s weight, temperature, pulse and blood pressure.  The veterinarian may listen to the dog’s heart and lungs using a stethoscope.  He may also check the patient’s eyes, ears and gums.

After the your companion’s physical examination, the veterinarian may recommend diagnostic testing.  The blood work that may be recommended include a complete blood count, serum chemistry profile, blood smear, reticulocyte count, slide agglutination test, and a direct Coombs test.

• Complete blood count - Can determine the patient’s platelet, red and white cell count and can also help determine if there is a bacterial infection; patients with IMHA will have a low red cell count, higher white cell count, low platelets and elevated liver enzymes
• Serum chemistry test - Evaluates organ functions and the electrolyte balance
• Blood smear - Can find abnormalities in blood cells; 89% of patients with IMHA have spherocytes, which are red blood cells shaped like spheres, instead of the normal disk shape
• Reticulocyte count test - Measures how fast red blood cells are made and released from the bone marrow
• Slide agglutination test - Can help determine if the red blood cells are being affected by an immune disease
• Coombs test - Can visualize/ detect the immune system’s antibodies on the surface of red blood cells

Other diagnostic tests that may help find the underlying reason for secondary IMHA are x-rays, ultrasounds, zinc toxicity test, urinalysis and polymerase chain reaction (PCR) assay.

If the patient’s red blood cell count is severely low, the veterinarian may suggest hospitalization. The patient can then receive 24/7 intensive care.  Once hospitalized your dog may receive a blood transfusion, supplemented oxygen treatment and medications.  Initial medications commonly used for treating IMHA are prednisone (corticosteroid) and doxycycline (antibiotic).  

Other medications that may be prescribed include azathioprine, cyclosporine, mycophenolate mofetil and Leflunomide.  These medications must be closely monitored because they can have adverse side effects (gastrointestinal tract irritation, nausea, susceptible to infections, lethargy).  Patients that do not respond to the immunosuppressive medications may need to have a splenectomy.  

Patients with secondary IMHA will also need to be treated for the underlying condition. The veterinarian will discuss with you what the best treatment plan is for the diagnosed condition.

There have been recent studies that show that some dogs may be slowly weaned off the medication after three months of treatment.  There is the possibility of relapse; 12 -24% of patients must be placed back on the medications.  Dogs that respond to the treatment plan have a fair prognosis.  Frequent follow up visits will be necessary to monitor the patient’s progress and to check for complications from the prescribed medications.