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Immune-mediated Hemolytic Anemia in Cats (IMHA)

Posted December 23, 2011 in Cat Diseases & Conditions A-Z

The red blood cells serve the crucial function of carrying oxygen to the cells in the body and picking up carbon dioxide. Anemia is a condition that arises when the number of red blood cells falls below normal values, or the red blood cells function improperly. There are many diseases and conditions that can cause anemia in cats. A low red blood cell count can be the result of blood loss, the destruction of the red blood cells, or an inadequate production of new red blood cells.

When your cat has IMHA, it means her immune system destroys its own red blood cells. Your cat’s body still produces red blood cells in the bone marrow to replace the destroyed cells, but once they are released into circulation, the immune system mistakenly recognizes them as something foreign, like a virus or infection, and destroys them. This condition is also referred to as autoimmune hemolytic anemia (AIHA).

There are two forms of IMHA: primary (or idiopathic), and secondary IMHA.
With primary IMHA, your cat's immune system mistakenly produces antibodies that attack its own red blood cells. This condition is fairly uncommon in cats.

With secondary IMHA, the surface of your cat’s red blood cells is modified by an underlying disease process, drug, or toxin. Your cat's immune system identifies the modified red blood cells as something foreign and destroys them. When too many red blood cells are destroyed and not replaced quickly enough by bone marrow, the patient becomes anemic.

Secondary IMHA can be triggered by a variety of conditions, such as:

Symptoms may include:

  • Pale gums
  • Acting tired, weak, or listless
  • Faster than normal pulse
  • Lack of appetite
  • Weight loss
  • Black/Tarry stools

These symptoms can vary from cat to cat and depend upon the underlying cause of IMHA. In some situations (mild or early IMHA), your cat may present no signs at all!

When a cat is anemic, it is important to identify the underlying cause. Your veterinarian may recommend different tests depending on your pet’s symptoms and history.

These tests may include:

  • A complete blood count to identify if your cat is anemic, and, if so, to determine whether or not her body is responding to the anemia by producing new red blood cells
  • A reticulocyte

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