Immune-Mediated Hemolytic Anemia

Liaison: Patti Emmett, MS, RN, CIC


Decreased numbers of red blood cells (RBCs) due to destruction by the immune system.

Signs and Symptoms

  • weakness and/or loss of energy

  • decreased interest in food

  • dark urine

  • pale gums

  • jaundice (yellow tinge in the whites of the eyes)

  • enlarged spleen

  • a slight fever may be present.


In many cases (60-70%), a cause isn’t found. In some cases, a primary reaction by the immune system precedes the act of red blood cell destruction.

The immune system (lymphocytes) begins to attack the body’s own RBCs with destructive antibodies. RBCs normally carry oxygen to tissues, and carry away waste. Iron and bilirubin are sent to the liver in larger amounts than normal causing jaundice and impaired liver function.

Altered liver function, lack of adequate tissue oxygen, and complications of blood clot formation can be life-threatening.

Risk Factors

Cancer (e.g. hemangiosarcoma) and drugs can trigger the immune system to overreact. (The immune system starts targeting proteins that resemble the drug; RBCs are destroyed as “innocent bystanders”). Examples of implicated drugs include trimethoprim-sulfa and methimazole.

Diagnostic Tests

Blood cell counts can determine if the numbers of red blood cells are normal or too low (anemia). Anemia can occur from bleeding or from increased RBC destruction (IMHA).

The bone marrow tries to make more RBCs to replace the destroyed, mature RBCs. Because the bone marrow can’t keep up with the destruction, immature forms of RBCs (“reticulocytes” and “nucleated RBCs”) may be released into the blood.

Additional testing can determine if the bone marrow is not responding. This may be temporary and resolve, or persist.

Treatment Guidelines

Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.

  • Prednisone and dexamethasone for immunosuppression.

  • Azathioprine if no response to above.

  • Transfusion when a crisis occurs.


  1. Barlough,J.E., Pedersen, N.C, 1995. “The immune system and disorders” in UC Davis School of Vet Med book of dogs. Siegal, M. Ed., p.331-333. Harper Collins, New York. three bones

  2. Hemolytic Anemia in the Merck Veterinary Manual. four bones

  3. two bones

  4. Kohn, B., 2003. Evans’ syndrome: immune-mediated hemolytic anemia in Immune-mediated thrombocytopenia-current approach. 28^th^ World Congress of World Small Animal Veterianry Assoc., Thailand. P. 1-3. four bones

  5. Trepanier, L.A., Danhof, R., Toll, J., and Watrous, D. 2003. Clinical findings in 40 dogs with hypersensitivity associated with administration of potentiated sulfonamides. [J Vet Int Med] 9; 17(5):p. 647-652. Link to abstract four bones

  6. Holloway, S.A., Meyer, D.J, and Mannella, C. 1990. Prednisolone and danazol for treatment of immune-mediated anemia, thrombocytopenia, and ineffective erythroid regeneration in a dog. [J Am Vet Med Assoc] 197 (8):1045-1048. Link to abstract three
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SCARF-Sponsored Research:

AKCCHF grant #00305: Histocompatibility Alleles Conferring Susceptibility to Canine Diabetes, Immune-Mediated Thyroiditis and Immune-Mediated Hemolytic Anemia.