Anemia: Immune Mediated Hemolytic Anemia (IMHA)


In immune-mediated hemolytic anemia (IMHA), the patient’s immune system attacks and destroys its own red blood cells. To better understand this disease, it helps to dissect the nomenclature. IMHA is an autoimmune disease, and “autoimmune" literally means the immunity against the self. "Hemolytic" is the destruction of red blood cells. “Anemia,” meanwhile, is defined as a decrease in the number of red blood cells or the amount of hemoglobin, resulting in a decrease in the oxygen-carrying capacity of the blood.

When the spleen and the rest of the immune system are functioning properly, it rids the body of old or damaged red blood cells. In IMHA, protein markers called antibodies stick to the red blood cells and cause the immune system to believe the red blood cells are like invading viruses or bacteria instead of parts of the body. This causes the immune system to attack the red blood cells and destroy them. When a large percentage of healthy red blood cells are tagged as “defective” and removed from the bloodstream by the immune system, the disorder is considered IMHA.

The underlying reasons the immune system mistakes the red blood cells for foreign bodies varies. In primary IMHA, the exact cause for the body’s attacks on red blood cells is unknown. Secondary IMHA occurs because an immune attack directed against an underlying condition such as a cancer, infection, or exposure to certain drugs or toxins causes the immune system to inadvertently destroy its own red blood cells. In this case, addressing the underlying cause while also treating the anemia is critical.

Whenever your pet is showing signs of a health issue, your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from immune-mediated hemolytic anemia or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital..

More Info

Both classifications of IMHA frequently affect dogs, with middle-aged female dogs three to four times more likely to be diagnosed with IMHA than males. Although all breeds can be affected, Cocker Spaniels are diagnosed more commonly with this disease than other breeds. There is strong evidence that IMHA is a genetic disease, which means it can be passed down through family lines. Primary IMHA is extremely rare in cats and shows no breed or sex predilection.

Clinical Signs

The symptoms of IMHA usually manifest themselves in the form of weakness, lethargy, decreased appetite, and an increase in the heart and respiration rate, and body temperature. These symptoms are cause by the massive, often sudden, depletion in red blood cells. One of the major functions of red blood cells is to carry oxygen from the lungs to all other tissues in the body. When there is an inadequate amount of red blood cells, the body becomes starved for oxygen.

Your pet might also become depressed and listless and exhibit panting, decreased appetite, weakness, or reluctance to exercise. You may also notice pale mucous membranes - such as those in the gums, ears, and eyelids - turning from a deep pink to a light rose or white.

Your dog may also appear to be jaundiced, or yellowed. This is most easily noticed in the whites of the eyes and is due to a buildup of bilirubin, a protein that is produced when hemoglobin - the protein that carries oxygen in red blood cells - is broken down within the body. Furthermore, your pet may vomit or have abdominal pain. You may also notice blood in the urine or stool. The symptoms of IMHA can appear suddenly or they may be gradual and progressive.