Anemia in Cats
Dr. Erika De Papp
A thorough history and physical exam are important in order to establish a diagnostic plan. Because there are so many causes of anemia, historical and physical clues are important to narrow down the possible diagnoses. The length of illness may allow estimation of how long the anemia has been present. Travel history, exposure to ticks, current or recent medications, vaccine history, and past medical problems may provide important information. Evaluation of the mucous membranes (gums, anus, vulva or penis) will often reveal pallor, which is suggestive of anemia. Abdominal distension and intra-abdominal fluid can often be palpated by an experienced clinician, which may lead to a diagnosis of blood loss into the abdomen. An enlarged spleen may be present with various types of anemia, and this can often be palpated as well. Complete blood count. The CBC evaluates the red and white blood cells, as well as the platelets. The CBC will confirm the presence of anemia. The white blood cell and platelet counts are also very important, because some diseases affect multiple cell lines. If all counts are low, this may be an indication of disease within the bone marrow. A high white blood cell count may be seen with inflammatory disease, cancer, infectious disease and immune-mediated disease. If the platelet count is severely low, this may be a cause of blood loss. The CBC is also an important means of evaluating red blood cell morphology. Certain cancers and immune-mediated diseases may cause characteristic changes in the red blood cell shape.
Additionally, careful examination for evidence of bruising or bleeding into the gut, eyes, nose, mouth, and ears can all be evaluated by the veterinarian. Yellow discoloration of the membranes or skin can be a marker of red blood cell destruction. This occurs due to rapid production of pigments that are a normal by-product of red blood cells. When cells are rapidly destroyed, the body becomes overwhelmed and the pigment (bilirubin) levels in the blood become elevated, imparting a yellow color to tissues.
Additional tests include:
Reticulocyte count. This is a measure of the number of immature red blood cells in circulation. This is a crucial test in evaluating an anemic animal, because it allows classification of the anemia. A normal bone marrow will respond to anemia by releasing immature red blood cells into circulation. This is called a regenerative anemia.
Regenerative anemia is caused by either blood loss or hemolyis (red cell destruction). Non-regenerative anemia is seen with either acute (very sudden) anemia of any cause, bone marrow disease, iron deficiency, or bone marrow suppression secondary to chronic disease or kidney failure. Performing a reticulocyte count is therefore very useful in narrowing down the causes of the anemia.
Biochemical profile. The biochemical profile provides important information with respect to overall organ function. For instance, it will aid in the diagnosis of chronic kidney failure, which is a common cause of anemia in older cats. It may also indicate abnormalities of the liver and endocrine organs.
Urinalysis. A urinalysis may reveal either blood in the urine or pigment changes, which are seen in cases of hemolytic anemia. It is important to interpret the urinalysis in light of the CBC and biochemical profile results. It also complements the biochemical profile in assessing kidney function.
Abdominal radiographs. Radiographs will provide good information with respect to organ size, and the presence of masses in the abdomen. Small masses may not be seen with routine radiographs. Fluid accumulation in the abdomen can also be noted on radiographs.
Abdominal ultrasound. Ultrasound often complements the findings on abdominal radiographs. It is a more sensitive means of examining the architecture of the abdominal organs, and pinpointing abnormal areas or masses. Ultrasound may also be useful to guide a fine needle aspirate of abnormal organs or to obtain any fluid present in the abdomen for analysis.
Thoracic radiographs. Radiographs of the thorax (chest) are important in cases where cancer is suspected, as the lungs are a common site of metastasis (spread of cancer) for many tumor types. Although metastatic disease can be present without showing up on the radiographs, the presence of metastasis in the lungs that is noted radiographically indicates that the disease has definitely spread to the lungs. Since all categories of anemia may be caused by cancer, thoracic radiographs are a common part of a work-up for anemia.
Coagulation profile. Tests of clotting function are imperative in animals with evidence of hemorrhage, either external or internal. Animals with hemolytic anemia are also prone to secondary bleeding disorders, so coagulation tests are useful for assessing most cases of regenerative anemia. Additionally, if the tests are abnormal, specific therapy may be indicated.
Bone marrow aspirate. This test is performed to obtain a sample of bone marrow cells for microscopic analysis. The bone marrow produces most of the red and white blood cells, as well as the platelets. Bone marrow evaluation is most useful in cases of non regenerative anemia, and in cases in which all cell lines are deficient. This test requires sedation or anesthesia for your pet, and is most commonly done at specialty hospitals.
Tests for infectious disease. Depending on the geographic location in which you live, certain infectious diseases may be likely to cause anemia. The infectious diseases likely to cause anemia in cats include hemobartonellosis, feline leukemia virus, and feline immunodeficiency virus. Additionally, certain fungal and protozoal infections can cause anemia as well.
Tests of immune function/dysfunction. A Coombs' test looks for antibodies directed against red blood cells. This test can sometimes be used to confirm a diagnosis of immune-mediated hemolytic anemia, although a negative test result does not rule out the disease. An anti-nuclear antibody test also evaluates for the presence of antibodies aimed at one's own cells and a positive test is another marker of immune-mediated disease.
Iron levels. If a patient has chronic blood loss, this can lead to iron deficiency. Iron deficiency is often suspected based on specific abnormalities seen in the CBC. Iron is important in the production of red blood cells, so iron deficiency will eventually cause a non-regenerative anemia. Various tests of iron stores can be evaluated if iron deficiency is suspected.
Genetic testing. There are rare genetic disorders documented in several breeds of cat that result in increased fragility of red blood cells, and can cause hemolytic anemia. In these cases, special genetic tests can be done to identify the abnormality. Abyssinian and Somali cats can be affected.
Blood type. A blood type is not important as a diagnostic tool, but is important information for patients requiring a blood transfusion. Similar to blood types in humans, the type allows the veterinarian to choose the appropriate blood donor so as to avoid an adverse reaction to the transfusion.