Anemia is a reduction in the normal number of red blood cells (RBCs), which are also called erythrocytes, or in the amount of hemoglobin in circulating blood. Hemoglobin is a protein molecule inside red blood cells that is critical to transportation of oxygen to all body tissues. There are a number of causes of anemia in domestic dogs, and it is important to ascertain why a dog is anemic before an appropriate treatment protocol can be developed.
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.
Prevention of Anemia in Dogs
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.
Within red blood cells is a protein called "hemoglobin," which functions to transport molecular oxygen in the blood to all body tissues. Normally, as red blood cells age or are damaged, they are broken down by other cells, called "macrophages." Part of the hemoglobin molecule is recycled to the bone marrow to be incorporated into new red blood cells (also called erythrocytes or RBCs). Other parts of the old or damaged RBCs are processed and excreted by the liver. When dogs have an abnormally low red blood cell mass – and therefore an abnormally low amount of hemoglobin available to carry oxygen throughout their bodies – they basically experience varying degrees of oxygen starvation. The consequences of anemia can be mild or life-threatening, depending on its cause and the ability of the dog's body to regenerate and maintain a healthy red blood cell level.
Symptoms of Canine Anemia
Owners may notice similar or slightly different signs of anemia depending on whether it comes on suddenly (acute anemia) or slowly (chronic anemia). Dogs suffering from anemia may have one or more of the following symptoms:
Lack of appetite
Pale mucous membranes (pallor); possible mucosal bleeding (primarily of the gums and nasal membranes)
Difficulty breathing (tachypnea); rapid shallow breathing; respiratory distress
Elevated heart rate (tachycardia)
Most of these signs are non-specific for anemia. However, when a number of them are present in one animal, anemia should be high on the list of suspects.
Dogs At Increased Risk
Dogs of all breeds, any age and either gender can be affected by anemia. Those with heavy parasite loads and with gastrointestinal ulcers are at increased risk of blood loss anemia. Hemolytic anemia (destruction of RBCs) due to varied hereditary defects are seen more so in certain breeds, including English Springer Spaniels and less commonly Cocker Spaniels (phosphofructokinase [PFK] deficiency), and in Basenjis, Beagles, West Highland White Terriers, Cairn Terriers, Miniature Poodles, Toy Eskimos and Dachshunds (pyruvate kinase [PK] deficiency). Greyhounds and Pit Bull Terriers appear to be predisposed to anemia caused by infectious agents.
Canine anemia is not particularly difficult to diagnose. Initially, the veterinarian will draw blood for a complete blood count (CBC), a packed cell volume (PCV) and a serum biochemistry panel, and probably will perform an analysis of the dog's urine as well. She also will evaluate a blood smear under the microscope to look closely at the structure of the red blood cells. A separate test is available to detect the presence of Ehrlicia canis, which is a blood-borne parasite in dogs. Another early test may be a coagulation panel and a buccal mucosal bleeding time test, to assess the clotting ability of the dog's blood. A fecal analysis can be done to check for what is called occult blood loss, which is blood loss through the intestines that is not visibly detectable otherwise.
How Anemia is Diagnosed
The initial data base described above will disclose red blood cell abnormalities in either quantity, quality or both if anemia is present. However, these tests will not necessarily identify the underlying cause of the problem. Advanced diagnostic tests include bone marrow aspiration and core bone marrow biopsy, if a problem with RBC production is suspected. These tests are performed under sedation or general anesthesia. The veterinarian may also take a sample of free fluid in the abdomen by a process called abdominocentesis. This involves placing a needle through the skin into the abdomen and drawing off a sample of any fluid that may be present. This test can reveal blood in the abdomen (called hemoabdomen) which may be secondary to trauma, bleeding disorders, disorders of the spleen or surgical suture failure. Other diagnostic tools include abdominal radiographs (x-rays), abdominal ultrasound and endoscopy (use of a tiny scope and camera to visualize the inside of the abdomen; useful to identify tumors, ulcers and the like). Specific tests are available to identify the presence of Mycoplasma and Babesia in the blood, and there are DNA tests to look for PK/PFK deficiencies that are seen in certain breeds. Finally chest films (thoracic radiographs) may be appropriate if cancer (neoplasia) is suspected.
Your veterinarian is best suited to determining which diagnostic tools should be used in any given case of suspected anemia. The causes of anemia are so variable that each dog must be assessed physically and in person before a diagnostic plan realistically can be developed.
When an owner suspects that his dog may be anemic based on his physical symptoms, he should take his dog to the veterinarian as quickly as possible. Depending on the underlying cause, anemia can become life-threatening if left untreated. The treatment goals are to provide supportive care while waiting for the bone marrow to kick back in (in cases of regenerative anemia); to control bleeding and restore blood volume and red blood cell numbers (in cases of blood loss anemia); to identify and resolve the underlying causes of chronic blood loss (iron deficiency, parasites, ulcers); and to provide good supportive care throughout the treatment process.
Of course, no one treatment protocol can be described for anemic animals, because the reasons for anemia are so varied. Speaking generally, veterinarians have a number of treatment options at their disposal depending upon the cause of anemia in the particular patient, including:
Intravenous fluid therapy to increase blood volume
Transfusions, with packed red blood cells, whole blood, platelets, fresh frozen plasma
Transfusion, bone marrow
Antibiotics, if infection is suspected; caution: trimethoprim sulfa has been known to cause aplastic anemia
Discontinue medications that may be contributing to aplastic anemia
Vitamin K1, for coagulation disorders
Dewormers/other antiparasitic medications
Iron dextran supplementation; ferrous sulfate administration
Potassium phosphate supplementation
Careful monitoring and follow-up are critical when managing anemic animals. However, depending on the underlying cause, the prognosis following treatment can be quite good. Cases of acute-onset aplastic anemia typically can be reversed within 3 to 4 weeks, once the causative agent is removed. Chronic aplastic anemia usually is more severe and can be more difficult to resolve, often taking months, after which recovery still may not happen. Younger dogs tend to have a better prognosis. Blood loss anemia carries a very good prognosis, once the bleeding (from surgery, trauma, parasites or otherwise) is stopped. Dogs with gastrointestinal ulcers have a fair prognosis, as do dogs with bleeding disorders, called coagulopathies. Anemia caused by cancer unfortunately carries a guarded to grave prognosis, depending on the patient's response to chemotherapy and/or surgical intervention. Dogs with hemolytic anemia – where something is damaging or destroying their red blood cells – usually recover well once the cause of hemolysis is removed and the dog is stabilized medically.