Autoimmune hemolytic anemia is a specific type of erythrocyte (red blood cell) deficiency in which the dog's immune system targets its own healthy red cells, accelerating their breakdown and removal.
Common name: Autoimmune hemolytic anemia Scientific name: Autoimmune hemolytic anemia, Primary immune-mediated hemolytic anemia, Idiopathic immune-mediated hemolytic anemiaDiagnosis
Signalment All breeds are susceptible to autoimmune hemolytic anemia, but cocker spaniels, Old English sheepdogs, poodles and Irish setters are predisposed. The disorder may occur at any age, but affected dogs are generally between two and eight years old. Female cases outnumber male cases four to one.
Incidence/prevalence Immune-mediated anemia is the most common cause of hemolysis, or destruction of red blood cells, in adult dogs. However the incidence of primary or autoimmune cases as compared to cases caused by infectious, parasitic, drug, toxic or cancerous agents is unknown.
Geographic distribution There is no known geographic predilection for this disease.
Clinical signs (primary, most to least frequent, scientific term, synonyms) Lethargy, weakness depression, anorexia (loss of appetite), pale mucous membranes (lips, gums, tongue), icterus or yellow tint to gums, skin and eyes , bilirubinuria (dark brown urine from hemoglobin release from damaged red cells), tachycardia (rapid heart rate), tachypnea (rapid respirations), dyspnea (difficult breathing from reduced oxygen secondary to red cell loss), gastrointestinal disturbances may briefly precede signs of anemia.
Clinical signs (secondary, most to least frequent, scientific term, synonyms) Splenomegaly (enlarged spleen), hepatomegaly (enlarged liver), heart murmur (abnormal heart sound) is sometimes detected. In rare cases where antibodies are activated during cold ambient temperatures, skin lesions can occur in the extremities.
Cause (scientific, common term) No inciting cause has been identified, genetic predisposition is possible, organ system affected (most to least affected), hematopoietic (red blood cells), immune (white blood cells), lymphatic and hepatobiliary (spleen, liver and bile ducts), integument (skin and nails).
Diagnostic tests Complete blood cell count can indicate source of anemia as blood loss, hemolysis or decreased red cell production. Blood smears allow visual identification of spherocytes (small red cells lacking central pallor), and evidence of erythrocyte clumping. These are common features of autoimmune hemolytic anemia.
Direct Coomb's test uses a blood sample to detect the presence of red cell bound antibodies that may damage erythrocytes but will not cause visible agglutination.
Serum biochemistry may indicate increased bilirubin, hemoglobin and liver enzymes.
Urinalysis can reveal the presence of hemoglobin or increased bilirubin in the urine.
Differential Diagnosis Other types of hemolytic anemia (Heinz body, parasitic, infectious, toxic, neoplastic), Enzyme deficiency anemias (pyruvate kinase, phosphofructokinase), Hepatobiliary disease (disorder of the liver and bile ducts).Overview
Autoimmune hemolytic anemia is a disorder of the dog's immune system in which antibodies fail to recognize normal erythrocytes as "self"; directly attacking and destroying them. The effect is a decreased number of erythrocytes in the circulation resulting in anemia once the hematocrit (percentage of red cells in whole blood by volume) drops to 37% or less.
Since the function of erythrocytes is to transport oxygen to the body's organs and tissues, the signs of anemia are due to insufficient oxygen in these tissues. Dogs exhibit weakness, lethargy, anorexia, depression and hypothermia. Gastrointestinal disturbances manifested by pica (chewing typically on non-food items), vomiting and diarrhea can precede signs of anemia. The tongue and gums may fade to pale pink or white. In severe anemia, breathing and heart rates become rapid and the dog may collapse during exercise. In some cases a heart murmur is detected because of decreased blood viscosity. The destruction of erythrocytes (red blood cells) releases hemoglobin and bilirubin into the plasma. Accumulation of these products causes a yellow tint to eyes, mucous membranes and skin. The spleen and liver can become enlarged while removing the damaged erythrocytes. Uncommonly during exposure to cold temperatures, a deadening of tissue can occur on the nose, ear tips, nail beds, and end of tail. Onset of signs is usually slow, but can occur suddenly.
While all dogs are susceptible to the disease, there is a predisposition among cocker spaniels, Old English sheepdogs, poodles and Irish setters. The disorder may occur at any age, but is generally seen in dogs between two and eight years of age. Female dogs are affected three to four times more frequently than males.Treatment
Home Care Cage rest or restricted activity may be necessary until the dog can be examined.
Professional Care A complete blood cell count will assist the veterinarian in determining if the anemia is due to hemolysis. Once this is determined, blood smears are examined for changes in erythrocyte structure, and evidence of autoagglutination or clumping of red cells. When the concentration of antibodies is too low to cause this direct agglutination, diagnosis is confirmed with another form of blood test called the direct Coomb's test. Finally, the veterinarian may need to rule out other causes of hemolytic anemia, such as infection, parasites, tumors and drugs or toxins.
Action Treatment is directed at preventing further erythrocyte destruction with use of corticosteroids and immunosuppressant drugs. Severe anemia is corrected with blood transfusions to maintain tissue oxygenation. Removal of the spleen may be beneficial, but only if tests prove the spleen is contributing to the hemolysis.
An understanding of the disease process and clinical signs is critical when the dog is treated as an out-patient. It is also imperative that clients become aware of medication side effects and remain in close contact with the veterinarian.
Outcome The response to treatment depends on the rate of hemolysis. Prognosis is guarded due to potential concurrent disease and complications. The mortality rate can reach 40%. In patients that survive a hemolytic crisis, life-long treatment may be needed and the disease can recur. Side effects of treatment may also be problematic. Ideally, the red blood cell count returns to normal.
Recommended Treatment Autoimmune hemolytic anemia is a life-threatening condition. See your veterinarian immediately for proper diagnosis and treatment of suspected autoimmune hemolytic anemia.
Fisher, DJ. Disorders of Red Blood Cells. In: Morgan, RV, ed.al. Handbook of Small Animal Practice. 4th Ed. Philadelphia: Saunders, 2003; 638-648.
Giger, U. Regenerative Anemias Caused by Blood Loss or Hemolysis. In: Ettinger, SJ & Feldman, EC, ed. Textbook of Veterinary Internal Medicine. 6th Ed. St. Louis: Elsevier Saunders, 2005; 1896-1901.
Thompson, JP. Systemic Immune-Mediated Diseases. In: Birchard, SJ & Sherding, RG. Saunders Manual of Small Animal Practice. 2nd Ed. Philadelphia: W.B. Saunders Co., 2000; 181-188.
Tillley, LP & Smith, FWK, Jr. The 5 Minute Veterinary Consult Canine and Feline. 2nd Ed. Philadelphia: Lippincott Williams & Wilkins, 2000; 434-435.
Giffin, JM & Carlson, LD. Dog Owner's Home Veterinary Handbook. 3rd Ed. New York: Howell Book House, 2000; 316-317.
Author Donna Lohman, DVM
Editor Steven Hansen, DVM, MS, MBA