Immune-Mediated Hemolytic Anemia (IMHA)

What is it?

IMHA, also called autoimmune hemolytic anemia (AIHA), is a disease in which the body attacks and destroys its own red blood cells. The bone marrow keeps making them, but they do not survive as long as they should. In about three-quarters of dogs, no trigger is found (primary IMHA). In others, it is set off by cancer (the most common secondary cause), infections such as Ehrlichia or Leptospira, blood parasites such as Babesia, drug reactions, snakebites, toxins, or bee stings.

What signs should I watch for?

Most dogs have severe anemia, with very pale gums instead of pink. They are listless, tire easily, and may faint or seem disoriented. Heart and breathing rates rise. As red cells break down, urine may turn dark, and the skin, gums, and whites of the eyes may turn yellow (jaundice). Vomiting and poor appetite can occur.

How is it diagnosed and treated?

A complete blood count shows low red cells, often with abnormal shapes and clumping. A Coombs test, a reticulocyte count, tests for infections, a chemistry profile, urinalysis, chest and abdominal X-rays, and abdominal ultrasound look for an underlying cause. A blood transfusion may be needed if the anemia is life-threatening. Secondary IMHA is treated by addressing the cause; primary IMHA is treated with immune-suppressing drugs such as prednisone, sometimes combined with azathioprine or cyclosporine. Because blood clots are a common complication, clot-preventing medication may be given. Referral to an internal medicine specialist may be recommended.

Can it be prevented, and what's the outlook?

• Primary IMHA cannot be prevented.
• Many dogs can be managed with the right medications, which are tapered slowly over several months once the anemia resolves.
• Relapses are common, so close monitoring is important as medications are reduced.