Immune Mediated Hemolytic Anemia (IMHA) in Dogs

Written by Small Door's medical experts

Immune mediated hemolytic anemia (IMHA) in dogs is a sudden, life-threatening illness that occurs when the body begins attacking its own red blood cells. IMHA requires immediate medical attention and treatment. As a pet parent, it’s a good idea to learn the signs and symptoms of this disease and know when to seek out veterinary care. It can help save your dog’s life.

In this article: 

What is anemia?

When there is a decrease in your dog’s total amount of red blood cells (RBCs, also known as erythrocytes), this is referred to as anemia. Red blood cells are important. Their primary function is to carry oxygen from the lungs to the other tissues throughout the body. The oxygen molecule attaches itself to an iron-rich protein on the RBC (which also gives these blood cells their red color) called hemoglobin. 

Causes of anemia can include blood loss (such as through injury or physical trauma), if your dog is not producing enough RBCs, or through RBC destruction (which can occur from such things as toxin ingestion, infection, or immune system defects). 

Anemia causes symptoms and often requires treatment depending on the severity and cause.

What is immune mediated hemolytic anemia (IMHA) in dogs?

Immune mediated hemolytic anemia is when your dog’s immune system becomes unable to recognize their own RBCs and marks them as a foreign threat to the body. Their immune system then begins attacking and removing its own red blood cells, causing severe anemia. This attack ruptures RBCs and is called hemolysis, hence “hemolytic anemia.” IMHA is the most common type of hemolytic anemia in canines. The condition causes a domino effect of life-threatening events:

  • Tissues and organs are starved of RBCs and are not able to receive enough oxygen to properly function and remove waste gasses from the body. 

  • As the oxygen within the body is not being properly transported, extra hemoglobin in the bloodstream damages the kidneys. 

  • The RBCs, now covered in antibodies, become sticky and adhere to one another, causing clots or embolisms in blood vessels. 

  • Lastly, the liver can become overwhelmed by an influx of bilirubin, which is the waste product of broken-down RBCs. 

When this happens, it is a life-threatening crisis and requires immediate medical attention. 

Roughly 20% to 75% of dogs lose their life due to IMHA, which is impacted by how severe it is, as the Merck Veterinary Manual states. 

Signs & symptoms of IMHA in dogs

Signs and symptoms of IMHA in dogs may include the following: 

  • Jaundice/icterus or yellowing of the skin and tissues (including the gums and eyes)

  • Pale gums or tissues

  • Dark, orange, or brown-colored urine

  • Decreased appetite (hyporexia)

  • Loss of energy or lethargy

  • Weakness

  • Hypotension (low blood pressure)

  • Fast/irregular heart rate (tachycardia)

  • Fever 

  • Enlarged spleen

What causes IMHA in dogs?

The cause is often unclear. Approximately 60% to 75% of IMHA cases do not have a known cause, as the Veterinary Information Network (VIN) states. 

Causes are sometimes classified as primary (occurring spontaneously) or secondary (occurring as a reaction, or in relation to, another underlying disease process or illness). These secondary causes may include:

  • Blood parasites

  • Cancers

  • Hereditary abnormalities

  • Bacterial or viral infections

  • Toxin exposure, such as certain foods, plants, drugs, and minerals

  • Reactions to drugs or vaccines 

The association between vaccination and IMHA is somewhat unclear, but vaccines may possibly overstimulate the immune system, leading to IMHA. Vaccines themselves have not been proven to cause IMHA. Your veterinarian can help you determine a vaccination cycle that is most appropriate for your dog.

Examples of some of the causes above include:

  • Heartworm parasite 

  • Tick-borne infections such as Ehrlichia 

  • Zinc found in pennies minted after 1982

  • Mothballs

  • Onions

There are also several canine breeds that are predisposed to IMHA:

  • Bichon Frise

  • Cocker spaniels

  • Collies

  • Doberman pinscher

  • English springer spaniel

  • Maltese

  • Miniature pinscher

  • Miniature schnauzer

  • Old English sheepdogs

  • Poodles

  • Irish setters

Can stress cause IMHA in dogs?

Stress is not a known cause for IMHA in dogs.

How do you diagnose IMHA in dogs?

Your veterinarian may recommend one or several of the following diagnostics if IMHA is suspected in your dog:

  • CBC: A complete blood count (CBC) will measure your dog’s red and white blood cells and platelets. 

  • Coomb’s test: Also referred to as a direct antibody test, this identifies the type of antibodies coating the surface of the RBCs.

  • Packed cell volume/total protein: The packed cell volume (PCV) will measure the percentage of RBCs within the total volume of blood. Total protein (TP) will measure the number of proteins present in the blood plasma. 

  • Coagulation profile: Prothrombin time (PT) and activated partial thromboplastin time (APTT) will show your dog’s ability to form blood clots and detect bleeding risk. 

  • Blood chemistry: A blood chemistry test will check the function of your dog’s organs. Your veterinarian will specifically be looking for abnormalities in your dog’s kidneys, liver enzymes, and bilirubin levels, which can indicate whether these organs are being affected by hemolysis or anemia. 

  • Flow cytometry: This test will look for the immunoglobulins IgG and IgM on the surface of red blood cells.

  • Blood parasite testing: This will test your dog’s blood for parasites, including heartworm disease and tick-borne diseases such as Ehrlichia and Anaplasma. 

  • Radiographs: Abdominal radiographs may be taken to better see your dog’s internal organs and check for whether there are any abnormalities or masses present that could be related to an underlying cause of IMHA.

  • Ultrasonography: An abdominal ultrasound can be used to visualize organs such as the kidneys, liver, and spleen. Ultrasonography offers a different perspective from radiographs and allows your veterinarian to obtain additional information. 

  • Urinalysis: A urine test will check your dog’s urine for blood, protein, infection, and pH levels, which can screen for underlying causes of IMHA.

Treatment for IMHA in dogs

Treatment of IMHA can vary depending on the severity of your dog’s symptoms and whether there are any underlying infections. Typically, treatment includes:

  • Immunosuppressive medications: Medications that lower the immune system response are used to help stop the destruction of RBCs. These medications can include prednisone, prednisolone, azathioprine, cyclosporine, chlorambucil, or mycophenolate.

  • Blood transfusion: A transfusion of packed RBCs is administered through an intravenous (IV) catheter. A transfusion consists of a unit of canine whole blood with plasma. Patients will be crossmatched with a canine blood donation (canine blood is grouped into two groups, antigen DEA 1 or DEA 7). Your dog will be constantly monitored throughout their treatment, so that your care team can watch for signs of any adverse reaction to the blood, such as an allergic reaction (hives, fever, or vomiting). A transfusion will take approximately 3 to 4 hours to complete.

Additional treatments include general supportive care (such as IV fluids and nutritional supplementation) and the administration of anticoagulants (such as heparin).

How long does it take to treat IMHA?

Treatment for IMHA may need to be continued for several months. Successful transfusions of RBCs can last in your dog’s body for approximately 3 to 4 weeks, and therefore your dog may need additional transfusions. Steroid therapies may be required for 4 months.

Is there a cure for immune mediated hemolytic anemia in dogs?

IMHA in dogs can be cured. However, there is an 11% to 15% chance of relapse, and some dogs may die from IMHA if it’s not caught and treated right away.

Is IMHA in dogs contagious for humans or other pets?

IMHA is an autoimmune condition and is not contagious or transmissible to humans. IMHA is also not contagious to other dogs.

However, some underlying infectious disease processes that may lead to IMHA can be contagious to other dogs and humans (such as bacterial infections like leptospirosis or protozoan infections such as Babesia spp). Leptospirosis can be transmitted to both animals and humans through contact with the urine of an infected animal. 

Most dogs are vaccinated against both viruses as part of the distemper/leptospirosis vaccine. Check with your veterinarian to make sure.

What is the cost of treating immune mediated hemolytic anemia in dogs?

The cost of treating IMHA in dogs can vary depending on the severity of symptoms and what treatment is needed. It may cost about $150 for a basic examination and medications to upward of hundreds to thousands of dollars more if further testing and supportive care is needed.

Recovery and management of immune mediated hemolytic anemia in dogs

Immediate and aggressive treatment is needed for IMHA patients. Approximately 1 in 5 dogs will experience a relapse of IMHA, and those who do recover will need to receive multiple blood transfusions, in addition to being on immunosuppressive medications for several months at a minimum.

Is IMHA in dogs fatal?

IMHA can be fatal in 20% to 75% of animals, as the Merck Veterinary Manual states, and it may reoccur. Rapid diagnosis and treatment are necessary.

How to prevent IMHA in dogs

Prevention is challenging because the cause is often unclear. It may not be possible to prevent IMHA. However, talk with your veterinarian about the best way to avoid secondary trigger causes, such as blood parasites, cancers, or reactions to drugs or vaccines. 

IMHA can also be prevented by making sure your dog is not exposed to toxins, including zinc found in pennies minted after 1982, mothballs, onions, and certain other foods and drugs.

Is there a vaccine for IMHA in dogs?

No, a vaccine for IMHA in dogs is not available. Talk with your veterinarian about vaccines for possible underlying causes of viral infections, such as leptospirosis. Vaccines may help protect your dog from severe infection and the development of IMHA.

Summary of immune mediated hemolytic anemia in dogs

IMHA is a sudden illness that can sneak up on your pet without a known cause. Being able to identify the signs and symptoms of this disease, followed by swift medical attention and treatment, can greatly help improve the survival outcome of your dog. Watch for signs such as tiredness, yellowing of the eyes, and dark urine, among others.

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