Hemolytic Anemia

Hemolytic anemia occurs when the circulating red cell lifespan is reduced due to the increased rates of red blood cell destruction (hemolysis). Hemolysis is the result of either of a defect in the red cells (inherent or acquired), or a defect of blood vessels through which red blood cells circulate.

Hemolysis can occur intravascularly (while the red cells are circulating) or extravascularly. Extravascular hemolysis involves the destruction and removal of damaged red cells by the killer cells (macrophages) of the spleen and liver, and the bone marrow is unable to compensate for premature destruction of red blood cells by increasing their production.

Types of Hemolytic Anemias in Dogs and Cats

There have been documented several types of hemolytic anemias in dogs and cats:

• Immune-mediated Hemolytic Anemia (IMHA), sometimes called autoimmune hemolytic anemia (AIHA), Red blood cells become coated with antibodies as they circulate. Antibody-coated red cells are removed by macrophages in the liver and spleen. Among the conditions that can cause IMHA are heartworm disease, lymphoma, lupus erythematosus, drugs, bee venom. Frequently, the cause of IMHA is unknown (idiopathic). In the cat, this type of IMHA is uncommon and is most often seen in association with FeLV infection. The clinical signs depend on the severity of anemia
• Heinz Body Anemia, Occurs in dogs and cats. Most cases of Heinz body anemia are the result of ingestion of oxidizing substances such as onions or the action of oxidizing drugs such as acetaminophen. Heinx bodies are precipitates of oxidized hemoglobin.

Most cases of AIHA are identified by blood test (a positive Coombs' test).

Causes

Babesia canis and B. gibsoni are protozoan red cell parasites in the dog that produce severe hemolytic anemia. Other erythrocyte parasites include B. bigemina, Eperythrozoon, and Anaplasma sp. Congenital hemolytic anemia in the Basenji dog resembles pyruvate kinase (PK) deficiency in man. Signs include lethargy, pale mucous membranes and dark wine-colored urine.

Treatment

The treatment of IMHA is directed against red blood cell destruction and formation of autoantibodies. Intensive supportive care is important, especially in severely affected animals. This includes vitamin supplementation and quality nutrition. As in all immune-mediated diseases, therapy is administered over a long period of time, and in some cases may be lifelong. Glucocorticoids are the most frequently used drugs for the treatment of IMHA. They have immunosuppressive and anti-inflammatory properties. In some animals glucocorticoids do not lead to the desired response, and more potent immunosuppressive agents must be added. Intravenous immunoglobulin (IVGG) therapy may be of value in dogs with immune-mediated hemolytic anemia that do not respond within 7 days of appropriate corticosteroid therapy.

Prognosis of Hemolytic Anemias in Dogs and Cats

Overall mortality is very high with this disease. Though treatment may cause the disease to go into remission for a while, a relapse is likely. Recovered cases should not be used for breeding.

References

1. Michael D. Lorenz, Larry M. Cornelius, Duncan C. Ferguson. Small Animal Medical Therapeutics
2. Alan H. Rebar. A Guide to Hematology in Dogs and Cats
3. Noble SJ, Armstrong PJ. Bee sting envenomation resulting in secondary immune-mediated hemolytic anemia in two dogs
4. Kellerman DL, Bruyette DS. Intravenous human immunoglobulin for the treatment of immune-mediated hemolytic anemia in 13 dogs