Causes of Canine Autoimmune Hemolytic Anemia
Autoimmune hemolytic anemia – also called immune-mediated hemolytic anemia, idiopathic nonregenerative immune-mediated hemolytic anemia, AIHA and IMHA - is a common disease in dogs that involves destruction of red blood cells (RBCs) by the dog’s own immune system. Why this happens is still a medical mystery. However, given the severity of the condition, owners should take this form of anemia very seriously.
There are several different classification schemes or subtypes of IMHA.
Primary or idiopathic IMHA involves antibodies produced by the dog’s immune system targeting and attacking its own red blood cells based on recognizing certain proteins, or antigens, which are part of the outer membrane surface of RBCs. Roughly 75% of the cases of autoimmune hemolytic anemia in dogs are thought to be caused by primary disease.
Secondary IMHA involves destruction of RBCs by antibodies based on so-called “novel antigens” that are exposed once the RBC membrane is damaged or altered due to cancer, infection, drug reaction, exposure to toxins, blood transfusion, venom from bee, snake or other bites or otherwise. Cancer is the most common cause of secondary IMHA in domestic dogs.
Intravascular IMHA is a condition where RBCs are destroyed by the immune system inside blood vessels.
Extravascular IMHA is where red blood cells are selectively destroyed in the dog’s liver and/or spleen.
A cascade of complicated events begins when the immune system identifies and targets an animal’s own red blood cells for destruction. While the intricate details of these medical events are beyond the scope of this article, suffice it to say that they are well-coordinated and may or may not culminate in the body’s ability to regenerate enough RBCs to bring the animal out of the anemic crisis.
Preventing Autoimmune Hemolytic Anemia
There is no realistic way to prevent autoimmune hemolytic anemia in dogs.
Unfortunately, an estimated 40% to 60% of dogs diagnosed with IMHA will die from the disease. Thromboembolisms, which are aggregations of blood factors including the elements that make up RBCs, are common consequences of autoimmune hemolytic anemia. The remnants from the breakdown of red blood cells (a thrombus) commonly form an embolism, which is a sudden blocking of an artery by a clot of foreign material that has traveled through circulation to become lodged where it shouldn’t be. Thromboembolisms obstruct normal blood flow through the vessels, depriving the body’s tissues of their necessary oxygen supply.