Causes of Canine Anemia
There are three general categories of anemia in companion animals: anemia due to blood loss (hemorrhagic or iron-deficiency anemia), anemia due to destruction of red blood cells (hemolytic anemia), and anemia due to insufficient production of red blood cells (aplastic anemia).
Acute blood loss, such as from trauma, surgery or other sudden bleeding disorders, causes anemia because there is a reduction in the overall number of circulating erythrocytes. Anemia can also be caused by slower, more chronic blood loss, such as from gastrointestinal bleeding due to ulcers, internal parasites, cancer (especially hemangiosarcoma) or external parasites (ticks, flea infestation), among other things.
Hemolytic anemia is caused by the destruction or abnormally short life-span of red blood cells, which leads to a low overall circulating red blood cell volume. Hemolytic anemia can be immune-mediated or non-immune mediated. Autoimmune hemolytic anemia is a condition in which the dog’s body for some reason perceives its own RBCs as being foreign and starts a cascade of immunological processes to destroy those cells. Non-immune-mediated hemolytic anemia is caused by destruction of RBCs by something other than the dog’s own immune system, such as by red blood cell parasites, hereditary diseases, toxins, extremely low circulating phosphorus levels or hereditary erythrocyte or enzyme defects.
Several different disorders can cause or contribute to anemia from insufficient production of red blood cells, called aplastic anemia. Healthy bone marrow is essential to production of RBCs. When the bone marrow fails to produce RBCs (and sometimes white blood cells as well) for any reason, the circulating number of RBCs is reduced. This is called aplastic anemia, and also is known as aplastic pancytopenia or hypoploastic anemia. It can be caused by tumors which infiltrate and occupy space within the bone marrow and by chronic kidney (renal) failure or other disorders which adversely affect production of erythrocytes. It also can be caused by infection such as by parvovirus and Ehrlichia, by certain drugs (chemotherapeutic agents, sulfa drugs, estrogen, phenylbutazone, etc.) and by exposure to radiation and/or toxins.
There is no way to categorically prevent anemia in domestic dogs. The causes of anemia are so varied and so fundamentally different from one another that prevention must be considered on a case by case basis. For example, the complete blood count (CBC) of dogs receiving medications known to be associated with hemolytic anemia should be monitored throughout the duration of that treatment. Blood loss anemia may be prevented by following good parasite control regimens and avoiding acute blood loss from accidents or injuries.
If a dog is able to re-boot its system and begin producing or replacing RBCs normally (called regenerative anemia), of course the prognosis is better. If the anemia is non-regenerative, treatment decisions and prognosis will be more variable.