Immune Mediated Hemolytic Anemia in Dogs (IMHA), Autoimmune Hemolytic Anemia
Dr. Leah Cohn
Expect your veterinarian to obtain a complete medical history. Be prepared for questions about what symptoms you have observed and how long they have been present, any medications your animal may have received, when the most recent vaccinations were given, and questions about the color of urine and stool.
A complete physical examination will be performed. Your veterinarian will evaluate the color of the gums and the eyes, palpate the abdomen looking for masses or swellings, and listen to the chest for heart murmurs or abnormal lung sounds.
A complete blood count (CBC) should be performed on all dogs suspected of having anemia (decreased number of red blood cells), regardless of the cause. This will not only quantify the number of red cells present, but will allow for a visual inspection of the cells under the microscope. Certain characteristic changes are often noted in the remaining red blood cells of animals with IMHA.
A "packed cell volume", or PCV, is a quick and simple test for the number of red blood cells present. Your veterinarian may do this test on a daily or near daily basis both initially and as therapy progresses to evaluate the balance between production of new cells and destruction of the old.
Reticulocyte counts allow the veterinarian to determine if new red cells are being made in appropriate quantities. The rapid production of new red cells is not only important for the animal, but helps the veterinarian rule out other causes of anemia from diagnostic consideration.
A serum biochemical profile and urinalysis may be performed to give clues as to possible causes of the anemia.
A saline agglutination test is a simple blood test that may show if the red cells are clumping together. In some forms of IMHA, the red cells actually stick together. If true agglutination is proven, it cements a diagnosis of IMHA.
A Coombs test is often indicated. A sample of the pet's blood is incubated with special reagents to look for evidence of an immune reaction to the blood. This test is very useful, but there are several causes of false positive results (for instance, prior transfusion) or of false negative results (for instance, prior corticosteroid therapy).
Coagulation tests such as the activated partial thromboplastin time, prothrombin time, fibrinogen, platelet count and/or fibrin degradation products) may be done to determine the ability of the blood to clot. Some dogs can develop a secondary condition called disseminated intravascular coagulation (DIC) which can cause a cascade of secondary problems. For more information on DIC, go to "Disseminated Intravascular Coagulation (DIC) in Dogs."
Newer, specialized tests search for evidence of an immune reaction to the red blood cells in more sophisticated ways that the traditional Coombs test. Direct immunofluorescence flow cytometry is an example of such a test; while this test is less likely to give a false negative result for an animal that has IMHA, it is also more likely to give a false positive result for an animal that does not have IMHA.
Radiographs, ultrasound examinations, or blood tests for infectious diseases may be indicated in some patients. These examinations may help rule out causes of anemia other than IMHA, or may help identify triggers that preceded development of IMHA.
Occasionally, IMHA destroys not only the red blood cells in circulation, but also the immature red cells being produced in the bone marrow. In this case, a bone marrow aspirate may be indicated. A large needle is placed in the bone while the animal is sedated, and a small sample of marrow is removed for microscopic analysis.