Immune-Mediated Hemolytic Anemia in Dogs (IMHA)
Mediated-Hemolytic-Anemia (Previously referred to as AIHA- Autoimmune Hemolytic Anemia)
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 dogs. 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 dog has IMHA, it means his immune system destroys its own red blood cells. Your dog’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 dog's immune system mistakenly produces antibodies that attack its own red blood cells. This is the most common cause of anemia in dogs.
With secondary IMHA, the surface of your dog’s red blood cells is modified by an underlying disease process, drug, or toxin. Your dog'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:
- Blood parasites
- Drug reactions
- Snake bites
- Exposure to certain chemicals and toxins
- Bee stings or other allergic reactions
Symptoms may include:
- Pale gums
- Acting tired, weak, or listless
- Shallow or rapid breathing
- Faster than normal pulse
- Lack of appetite
- Weight loss
- Black/Tarry stools
- Eating dirt
These symptoms can vary from dog to dog and depend upon the underlying cause of IMHA. In some situations (mild or early IMHA), your dog may present no signs at all!
When a dog is anemic, it is important to identify the underlying cause. Your veterinarian may recommend particular tests, depending on your pet’s symptoms and history. These tests may include:
- A complete blood count to identify if your dog is anemic, and, if so, to determine whether or not his body is responding to