Autoimmune Hemolytic Anemia in Dogs

By Tammy Hunter, DVM; Ryan Llera, BSc, DVM; Cheryl Yuill, DVM, MSc, CVH

What is anemia?

Anemia is not a specific disease, but rather a symptom of some other disease process or condition. Anemia is a medical term referring to a reduced number of circulating red blood cells (RBCs), hemoglobin (Hb), or both.

Red blood cells are produced in the bone marrow and then released into circulation. As the red blood cells age or become damaged, they are removed from the bloodstream and recycled to form new red blood cells. The number of circulating red blood cells may decrease if fewer are produced in the bone marrow; if more are destroyed (lysis); or if more are lost from circulation, as seen with hemorrhage (bleeding).

Hemoglobin delivers oxygen to the cells and tissues of the body, and a dog who is anemic will show symptoms related to a lack of oxygen.

What is autoimmune hemolytic anemia (AIHA)?

Autoimmune means an immune reaction directed against the body's own tissues, while hemolysis comes from the Greek words “hemo”, meaning blood, and “lysis”, meaning to break open. Autoimmune hemolytic anemia (AIHA) is an immune system disease in which the body attacks and destroys its own red blood cells.

In dogs with AIHA, red blood cells are still being manufactured in the bone marrow, but once released into circulation, they have a shorter-than-normal life span.

This disease may also be called immune-mediated hemolytic anemia or IMHA.

What causes autoimmune hemolytic anemia?

AIHA may be primary (idiopathic) or it may be secondary.

With primary AIHA, the dog's immune system is not working properly and it incorrectly makes antibodies that target its own red blood cells. In dogs, it is estimated that about three-quarters of cases of AIHA are primary.

With secondary AIHA, the surface of the red blood cells is altered by an underlying disease process or a toxin. The dog's immune system recognizes the altered red blood cells as “foreign” invaders that must be destroyed. Secondary AIHA may be triggered by various conditions:

  • cancer
  • infections as seen with Ehrlichia or Leptospira (see handouts “Ehrlichiosis in Dogs” and “Leptospirosis in Dogs”)
  • blood parasites such as Babesia (see handout “Babesiosis in Dogs”)
  • drug reactions
  • snakebites (see handout “Snakebite Envenomization”)
  • chemicals, toxins, or bee stings
  • events that are stressful on the body (if underlying secondary causes are already present)

In dogs, cancer appears to be the most common cause of secondary AIHA.

Once targeted, the red blood cells are either destroyed within the blood vessels by a process called intravascular hemolysis or destroyed when they circulate through the liver or spleen by a process called extravascular hemolysis. In both situations, hemoglobin is released; the liver will attempt to break down the excess levels of hemoglobin, increasing the workload on this organ.

What are the symptoms of AIHA?

Most dogs with AIHA have severe anemia, and their gums are very pale, rather than the normal pink to red color. Dogs with anemia are listless and tire more easily; these symptoms occur because there are not enough red blood cells to carry oxygen to the tissues. The dog may faint or appear disoriented due to low oxygen levels in the brain. To compensate for the lack of oxygen to the tissues, heart rate and breathing rate will increase.

"Most dogs with AIHA have severe anemia, and their gums are very pale,
 rather than the normal pink to red color."

As the disease progresses, excessive levels of bilirubin, a breakdown product of red blood cell hemolysis, build up within the body. Some of this excess bilirubin spills over into the urine, causing it to appear dark. Excessive levels of bilirubin cause the skin, gums, and other mucous membranes to appear yellow or jaundiced. The dog may vomit or may have a poor appetite.

How is AIHA diagnosed?

Anemia is diagnosed by performing a blood test called a complete blood count (CBC). The CBC measures several different values in a sample of whole blood. To test for anemia, packed cell volume (PCV) is measured to determine the percent of red blood cells in the sample; the number of red blood cells are counted; and the cells are examined under a microscope to determine their size and shape.

With AIHA, both the number and percent of red blood cells will be low and the size and shape of the cells will be abnormal. In many cases of AIHA, there will also be evidence of “autoagglutination” or abnormal clumping of red blood cells.

If AIHA is suspected, your veterinarian will recommend additional diagnostic tests to determine whether the disease is primary or secondary. Tests may include a reticulocyte test to detect the number of reticulocytes (immature red blood cells) in the bloodstream; antibody tests such as a Coombs test; and serologic blood tests to detect certain diseases (e.g., babesiosis, leptospirosis, ehrlichiosis, or heartworm).

What other tests are important with this disease?

Your veterinarian will recommend additional tests to evaluate the overall health of your dog and to detect any underlying cause for secondary AIHA. Recommended tests usually include a biochemical profile, a urinalysis, X-rays of the chest and abdomen, and an abdominal ultrasound examination. Depending on your pet's individual results, other tests may also be recommended.

"Your veterinarian will recommend additional tests to evaluate the overall health of your dog and to detect any underlying cause for secondary AIHA."

The biochemical profile will evaluate organ function and electrolyte levels, while the urinalysis will provide a baseline measure of kidney function and indicate whether there is evidence of an infection in the urinary tract. Chest X-rays help detect or exclude the presence of cancer in the lungs, while abdominal X-rays or ultrasound help detect or exclude the presence of cancer within the abdomen.

How is AIHA treated?

If your dog's anemia is so severe that it is life-threatening, a blood transfusion will be needed. Before giving a transfusion, your veterinary team will take blood samples for cross matching (like blood typing). The main purpose of a blood transfusion is to stabilize the dog while the underlying cause of the anemia is determined and other treatments can begin to take effect.

If the AIHA is secondary, the treatment will be directed at the underlying cause and may include various antibiotics, heartworm treatment, or toxin antidotes, if available.

If no underlying cause can be detected, or if the disease is determined to be primary or idiopathic AIHA, immunosuppressive therapy will be used. In some cases of idiopathic AIHA, the dog will respond rapidly to treatment with immunosuppressive doses of corticosteroids (usually prednisone). In other cases, the patient may require a combination of immunosuppressive medications, such as azathioprine or cyclosporine, to get the condition under control. Since thromboembolisms (blood clot-induced blood vessel obstructions) are common complications of AIHA, dogs may also be started on medications such as clopidogrel (Plavix®) or acetylsalicylic acid (Aspirin®). 

Your veterinarian will outline a treatment plan specific for your dog's needs, based on diagnostic test results. With complex cases, your veterinarian may recommend a referral to an internal medicine specialist.

What is the prognosis for AIHA?

The prognosis for dogs with AIHA is based on the specific diagnosis, as well as the dog’s general condition at the time of diagnosis. In many cases, the patient's condition can be managed with the appropriate drug treatments.

Once the patient's condition improves and the anemia resolves or stabilizes, your veterinarian will recommend tapering off the immunosuppressive medications over a period of several months to lessen any side effects associated with therapy. Since relapses are common with this disease, you will need to monitor your dog closely as medications are decreased or discontinued.

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