Anemia - is a deficiency of red blood cells, and may result from many causes including bleeding, failure to produce enough new red blood cells, or destruction of existing red blood cells.
Hemolysis -  refers to the lysis, or destruction, of the red blood cells ("heme" is an essential component of red blood cells that allows them to carry oxygen).
Immune mediated - simply states that in these cases the process of red blood cell destruction is carried out by the immune system.
Immune mediated hemolytic anemia (IMHA), also known as auto-immune mediated hemolytic anemia (AIHA), is a disease in which the body's immune system, which is designed to attack and kill germs, attacks and kills the body's own red blood cells. The attack begins when antibodies, which are molecules made by the immune system to target germs, instead attack the animal's own red blood cells for destruction. The red blood cells carry oxygen to the tissues, and the animal cannot survive without adequate oxygenation of the tissues.
With severe anemia of any cause, the tissues are unable to receive adequate oxygen. In cases of IMHA, destruction of red blood cells results in a sudden and often very severe decrease in red blood cell numbers. Although there is usually a substantial increase in the number of new red blood cells produced within the bone marrow, production of new cells cannot keep up with the rapid destruction of cells. Unless the immune system's attack on the red cells can be curbed, the animal will die. Swift treatment may stop the attack, allowing the newly made red blood cells to replace those that were destroyed. Unfortunately, it is not always a simple matter to stop the immune attack, and there are many potential complications of IMHA. Although many animals treated for IMHA go on to live full lives, even those who receive appropriate therapy may succumb to the disease.
IMHA is a rapidly life-threatening disease. Even with appropriate treatment, this disease can be fatal.
IMHA occurs more often in dogs than in cats, in middle-aged animals (3 to 8 years old), and in more females rather than males. While any breed can be affected, certain breeds develop IMHA more often than others do, such as the Cocker Spaniel, Springer Spaniel, Miniature Poodle, Finnish Spitz, Irish Setter, Dachshund, Bichon Frise and Old English Sheepdog.
What Causes IMHA?
The causes of IMHA remain largely unknown. While some cases of IMHA may be associated with a triggering event (cancer, infection, and perhaps even vaccinations), these events do not explain why the immune system misdirects its arsenal of weapons against the animal it is meant to protect.
Types of IMHA
There are different forms of IMHA;
  • Primary –also known as idiopathic, results from the antibody attacking the red blood cell membrane. There is no known underlying cause or trigger for this type of IMHA. Most cases of IMHA in dogs (over 75%) are categorized as primary.
  • Secondary – results from the antibody attacking a membrane antigen that is exposed because of anunderlying disease. Underlying causes that can expose the membrane may include neoplasia (cancer), infections, reactions to drugs, toxins, allergic reactions to bee stings and blood transfusions. The most common cause for secondary IMHA is cancer. Possible drug triggers may include antibiotics (such as sulfonamides, cephalosporins, penicillins), vaccines and procainamide.
  • Intravascular – means that the red blood cells are being destroyed in the blood vessels.
  • Extravacular – means that the red blood cells are being destroyed outside of the blood vessels, most commonly destroyed by macrophages in the spleen and/or liver.
Symptoms - What To Watch For
  • Pale gums ·  Yellow tinged gums or whites of the eyes
  • Dark or dark yellow urine ·  Tiring easily, weakness
  • Lethargy ·  Loss of appetite
  • Vomiting ·  Tachypnea (rapid breathing)
How is IMHA Diagnosed?
  • Complete history and medical examination - be prepared for questions about any medications your pt may have received, when the most recent vaccinations were given, and questions about the color of urine and stool.
  • Complete blood count (CBC)  - should be performed on all dogs suspected of having anemia (decreased number of red blood cells), regardless of the cause.  This should included a Reticulocyte count, which determines if new red cells are being made in appropriate quantities.  In addition a blood smear should be looked at under the microscope.
  • Serum biochemical profile and urinalysis  - may be performed to give clues as to possible causes of the anemia.
  • PCV  or packed cell volume -  quick and simple test for the number of red blood cells present.
  • Saline agglutination test - simple blood test that may show if the red cells are clumping together.
  • Coombs test - looks for evidence of an immune reaction to the blood.
  • Radiographs, ultrasound, or blood tests for infectious diseases -  may be indicated in some patients. These examinations may help rule out causes of anemia other than IMHA, or may help identify triggers that preceded development of IMHA.
Treatment of IMHA involves both direct attempts to halt the immune system attack on the red blood cells, and supportive care. The immune system is a complicated network of cells and cell products all designed to protect the body from foreign invaders. As with any complicated system, there are multiple places where errors can occur. When these errors result in the destruction of red blood cells (that is, IMHA), the immune system's attack must be halted if the animal is to survive. Unfortunately, the drugs available to halt the attack are not specific, meaning that they not only diminish the attack on the red blood cells, but also interfere with appropriate immune response to germs. This puts the animal undergoing therapy for IMHA in the precarious position of needing just enough, but not too much, immune suppression.
The drugs available to suppress the immune system interfere with entire pathways of immunity, and occasionally more than one of these paths must be interrupted to stop destruction of the red blood cells. In most dogs that respond successfully to therapy, the dose of immunosuppressive drugs can be very gradually lowered. Some animals will eventually be able to discontinue medications altogether, while others will require life-long therapy.
All immunosuppressive therapies require time to take effect. Until the destruction of red cells can be halted, supportive care is crucial for the animal's survival.
  • Corticosteroids - (prednisone, prednisolone) suppress the immune system's attack on the red cells by several mechanisms and are the mainstays of treatment for IMHA. While the effect of corticosteroids is more rapid than that of many other immunosuppressive drugs, it is still often 3 to 5 days before a positive response may be seen. Initial dosages of corticosteroids are very high, and may be associated with unpleasant side effects such as increased thirst and appetite, along with increased urination and weight gain. The dosage will be slowly decreased over several months after the animal improves.
In the most severe cases, or those cases that fail to respond to corticosteroids, other immunosuppressive agents may be utilized. These include drugs such as:
  •  Azathioprine - is toxic to the type of immune cell (lymphocytes) that produces antibodies. By destroying some of these cells, less antibody is produced to both red blood cells and to germs. It takes at least a week to become effective.
  • Cyclophosphamide - is another drug that is toxic to lymphocytes, and it is also used to treat lymphatic cancer. In the small number of studies where it has been evaluated, the response of IMHA to cyclophosphamide has been very disappointing.
  • Cyclosporine - is the same drug used to prevent rejection of transplanted organs. It suppresses immunity by affecting molecules known as cytokines that are secreted from immune cells.  
  • Supportive care - is essential to the successful treatment of IMHA. Such care may include blood transfusion, nursing, and medications.  Intravenous fluids are rarely used but may be indicated to prevent dehydration in some pets.
  • Heparin - is a medication that helps prevent formation of these clots.  Complications of IMHA include the formation of blood clots.
Home Care
It is crucial to administer all prescribed medications as directed. Even one missed dose can have serious consequences.
Limit your pet's activity. Anemic animals should not be encouraged or expected to engage in active play.
Provide adequate nutrition. Encourage the pet to eat a well-balanced pet food, but we can suggest appropriate enticing treats for the pet that refuses food.
The prognosis depends on the pet's response to treatment and the diagnosis and treatment of any possible underlying cause for the disease. The prognosis is generally considered poor. The mortality rate is estimated to be 40 to 60% in dogs. Some dogs may relapse within the first year.

Optimal treatment for your pet requires a combination of home and professional care.

  • Alert us if you are experiencing problems treating your pet. Even a few missed doses can have disastrous results.
  • Expect to return for frequent blood tests in the early days of treatment. As your pet responds to therapy, the red blood cell count is expected to improve. Once near normal levels, the drug dosages can be slowly decreased. We will need to check the red blood cell count after each adjustment to therapy.
  • You should expect that a pet receiving corticosteroids will experience an increase in thirst, and with that, an increased frequency of urination.
  • Most pets receiving corticosteroids will also experience an increased appetite. Monitor what your pet eats, and place limits on food consumption. Pets on corticosteroids often gain large amounts of weight over a short period of time.
  • Because the pet is treated with drugs to suppress the immune system, they may be prone to developing infection. If you notice lethargy, inappetence, vomiting, diarrhea, or urinary accidents in the house, please let us know as soon as possible.

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