Symptoms and Treatments of Anemia in Dogs
Anemia is a defined as a deficiency of red blood cells (erythrocytes) in the circulatory system. Adult dogs are anemic when the concentration of red cells in whole blood is less than 37 percent by volume. The normal range is 39 to 60 percent. Red cells are produced by the bone marrow and have an average life span of 110 to 120 days. Old red cells are trapped by the spleen and removed from the circulation. The iron they contain is recycled to make new erythrocytes.
The purpose of red blood cells is to carry oxygen. Thus, the symptoms of anemia are caused by insufficient oxygen in the organs and muscles. Signs include lack of appetite, lethargy, and weakness. The mucous membranes of the gums and tongue become pale pink to white. In dogs with severe anemia, the pulse and respiratory rate are rapid, and the dog may collapse with exertion. A heart murmur may be heard.
Anemia can be caused by blood loss, hemolysis, or inadequate red blood cell production.
In adult dogs the most common causes of blood loss are trauma, slow gastrointestinal bleeding associated with stomach and duodenal ulcers, parasites, and tumors in the gastrointestinal tract. Chronic blood loss also occurs through the urinary system. Hookworms and fleas are common causes of chronic blood loss in puppies.
Treatment: Treatment must be directed toward the cause of the anemia. Gastrointestinal bleeding can be detected by checking the stools for microscopic traces of blood. Urinalysis will pick up traces of blood in the urine that may not be visible to the naked eye. Other tests can also be used to determine the cause of the occult (microscopic) bleeding.
Hemolysis is an acceleration in the normal process of red blood cell breakdown. Red blood cells break down to form bile and hemoglobin. With severe hemolysis, these breakdown products accumulate in the body. Accordingly, in a dog experiencing an acute hemolytic crisis you would expect to see jaundice and hemoglobinuria (passing dark-brown urine that contains hemoglobin). In addition, the dog appears weak and pale and has a rapid pulse. The spleen, liver, and lymph nodes may be enlarged.
Causes of hemolysis include immune-mediated hemolytic anemia, congenital hemolytic anemia, infectious diseases (such as canine babesiosis and leptospirosis), drug reactions to medications such as acetaminophen, and poisonous snake bites. A number of bacteria produce toxins that destroy red blood cells, so hemolysis can also occur with severe infections.
Immune-Mediated Hemolytic Anemia
This is the most common cause of hemolysis in adult dogs. Red blood cell destruction is caused by auto-antibodies that attack antigens present on the surface of the cells, or by antigens from medications or organisms attached to the red blood cell walls. The weakened cells are trapped in the spleen and destroyed.
Poodles, Old English Sheepdogs, Irish Setters, and Cocker Spaniels are predisposed to immune-mediated hemolytic anemia, but all breeds are susceptible. Affected dogs are usually between 2 and 8 years of age; females outnumber males four to one.
Most cases of immune-mediated hemolytic anemia are idiopathic. That is, the reason why the auto-antibodies developed in that particular dog is unknown. In some cases there is a history of recent drug therapy. An immune-mediated hemolytic anemia also occurs with systemic lupus erythematosus.
The diagnosis is made by microscopic examination of blood smears, looking for specific changes in the appearance of the erythrocytes and other blood elements; and by serologic blood tests.
Treatment: Treatment of idiopathic immune-mediated hemolytic anemia is directed toward preventing further red cell destruction by blocking the antigen-antibody reaction using corticosteroids and immunosuppressants. Severe anemia is corrected with blood transfusions. Splenectomy (removal of the spleen) may be beneficial, but only when tests prove that the spleen is contributing to the hemolytic process.
The response to treatment depends on the rate of hemolysis and whether an underlying cause can be found and corrected. The outlook is guarded; even with appropriate medical treatment, the mortality rate is close to 40 percent.
Congenital Hemolytic Anemia
Several inherited abnormalities in the structure of red blood cells can result in their premature destruction. Phosphofructokinase deficiency is an autosomal recessive trait that occurs in English Springer Spaniels and Cocker Spaniels. A deficiency of this enzyme results in changes in the pH of red blood cells, causing the cells to periodically fragment and produce bouts of hemoglobinuria. There is no effective treatment.
Pyruvate kinase deficiency is another red blood cell enzyme deficiency caused by an autosomal recessive gene. This disease is recognized in several breeds, including Basenjis, Beagles, and West Highland White Terriers. Puppies usually develop the hemolytic anemia at 2 to 12 months of age. Death by age 3 is the usual outcome.
Genetic tests for phosphofructokinase and pyruvate kinase deficiency are available through the University of Pennsylvania at PennGen, and from OptiGen and VetGen.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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