Immune Mediated Hemolytic Anemia (IMHA) in Cats

Written by Small Door's medical experts

Immune mediated hemolytic anemia (IMHA) in cats is a critical, life-threatening illness that occurs when your cat’s immune system begins attacking its own red blood cells. IMHA requires immediate medical attention and treatment. Read on to identify the signs and symptoms of this disease so you can seek out veterinary care right away, and learn about IMHA causes, diagnosis, treatment, and prevention.

In this article: 

What is anemia?

Anemia is what occurs when there is a decrease in the number of red blood cells (RBC, also known as erythrocytes) in your cat’s body. The primary function of these cells is to carry oxygen from the lungs to the other tissues in the body. For this to happen, an oxygen molecule will attach itself to an iron-rich protein on red blood cells (which also gives these blood cells their red color) called hemoglobin. 

Anemia can be caused by blood loss (such as through physical trauma or injury), RBC destruction (which can occur from such things as toxin ingestion, infection, or immune system defects), or through the body merely not producing enough RBCs. 

Anemia often causes symptoms, and once the cause is determined, it can be treated.

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

Immune mediated hemolytic anemia is a condition in cats when the body begins attacking and removing its own red blood cells, causing severe anemia. This occurs because your cat’s immune system becomes unable to recognize its own cells and sees them as a foreign threat to the body. The immune system then creates antibodies whose job is to specifically attack and destroy the RBCs circulating throughout the body. This process of RBC destruction, or cell rupture, is called hemolysis. It causes a series of life-threatening problems in the body:

  • Due to the decreased number of RBCs, the tissues and organs 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, an excess of hemoglobin within the bloodstream damages the kidneys. 

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

  • Additionally, the liver becomes 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. 

Approximately 20% to 75% of animals who are diagnosed with IMHA will lose their life to the disease, the Merck Veterinary Manual states.

Signs & symptoms of IMHA in cats

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

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

  • Loss of energy or lethargy

  • Weakness

  • Dark, orange, or brown-colored urine

  • Pale gums or tissues

  • Fever 

  • Decreased appetite (hyporexia)

  • Enlarged spleen

  • Tachycardia or fast/irregular heart rate

  • Hypotension or low blood pressure

What causes IMHA in cats?

IMHA can either have a primary cause (a spontaneous onset of no apparent underlying etiology) or secondary (caused by, or related to, another disease process or illness). Approximately 60% to 75% of IMHA cases in dogs and cats do not have any apparent underlying cause.

Most often in cats, IMHA is caused by either an infectious blood parasite, Mycoplasma haemofelis, or from the feline leukemia virus (FeLV). 

Additionally, causes of IMHA may include:

  • Cancers

  • Bacterial infections

  • Hereditary abnormalities

  • Toxin exposure

  • Reactions to drugs or vaccines

It should also be noted that while some studies have shown an association between vaccination and IMHA, possibly from overstimulation of the immune system, vaccines themselves have not been proven to cause IMHA. Your veterinarian can help you determine a vaccination cycle that is appropriate for your cat.

Other examples of these feline causes include:

  • Protozoan infections such as Babesia spp or Cytauxzoon spp

  • Toxins such as aspirin, acetaminophen, copper, zinc, onions, red maple, and oak 

Can stress cause IMHA in cats?

There are no studies indicating that stress causes IMHA in cats.

How do you diagnose IMHA in cats?

If IMHA is suspected in your cat, your veterinarian may recommend one or several of the following diagnostics:

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

  • Coomb’s test: Also known as a direct antibody test, this identifies the type of antibodies that are 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 within the blood plasma. 

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

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

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

  • Blood parasite testing: This will test your cat’s blood for parasites, including heartworm disease and Mycoplasma

  • Urinalysis: A urinalysis will check your cat’s urine for blood and protein, infection, and pH levels, which could be indicative of anemia or another underlying infection or disease process that may cause or be related to IMHA.

  • Radiographs: Abdominal radiographs may be taken to visualize your cat’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. 

Treatment for IMHA in cats

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

  • Blood transfusion: A transfusion of packed RBCs is administered through an intravenous (IV) catheter. A transfusion consists of a unit of feline whole blood with plasma. Your cat will be crossmatched with a feline blood donation (feline blood is classified into three groups, A, B, and mic). Your cat will be constantly monitored throughout the treatment, so that the medical 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.

  • Immunosuppressive medications: Immunosuppressive medications are used to help stop the destruction of RBCs. These medications can include prednisone, prednisolone, cyclosporine, chlorambucil, or mycophenolate.

Other treatments may 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, and there is a chance of relapse. Successful transfusions of RBCs can last within a cat’s body for approximately 3 to 4 weeks, and therefore your cat may need additional transfusions. Steroid therapies may be required for 4 months.

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

IMHA in cats can be cured some of the time. However, there is an 11% to 15% chance of relapse, as VIN states, and some cats may lose their life from IMHA.

Is IMHA in cats contagious for humans or other pets?

IMHA is not contagious or transmissible to humans, as it’s an autoimmune disease. IMHA is also not contagious to other cats. However, some underlying infectious disease processes can be contagious to other cats and humans (such as bacterial infections like feline leukemia or protozoan infections such as Mycoplasma). 

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

The cost of treating IMHA in cats 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 cats

Aggressive treatment is needed for IMHA patients. Approximately 1 in 5 cats will experience a relapse of IMHA, and those that do recover will need to be on immunosuppressive medications for a minimum of several months, in addition to receiving multiple blood transfusions.

Is IMHA in cats fatal?

IMHA may be fatal in 20% to 80% of cats. 

How to prevent IMHA in cats

Most of the time, IMHA cases do not have any apparent underlying causes. But sometimes, secondary to things – such as blood parasites, cancers, or reactions to drugs or vaccines – can play a role. Discuss with your veterinarian ways to avoid these triggers. 

IMHA can also be prevented by making sure your cat is up to date on their vaccinations and parasite prevention, and that they’re not exposed to toxins, such as oak, red maple, and onions.

Is there a vaccine for IMHA in cats?

There is not a vaccine for IMHA in cats. There are vaccines for possible underlying causes of viral infections, such as feline leukemia. While vaccines may not prevent infection, they can minimize the severity of symptoms should your cat contract feline leukemia.

Summary of immune mediated hemolytic anemia in cats

While IMHA is a life-threatening emergency, knowing what toxins your cat should avoid, keeping them up to date with their vaccinations and parasite prevention, and knowing what signs and symptoms to look out for can help save your cat’s life.

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