Anemia in Dogs

In dogs, the most common cause of hemolytic anemia is immune mediated. This type of anemia can occur on its own or as a result of tumors, infection, drugs, or vaccinations. The body no longer recognizes red blood cells as self and develops antibodies to circulating red blood cells, leading to their destruction.

Dogs with immune-mediated hemolytic anemia are usually jaundiced, sometimes have a fever, and may have an enlarged spleen. They can show mild, slow-developing signs and not appear to be in any pain, or they can suddenly be in severe crisis. Your veterinarian will tailor treatment to the animal’s signs. Any underlying infections will be treated and unnecessary drug therapy discontinued. Intravenous fluid therapy may be started and supplemented with blood transfusions if necessary. Drugs are also given to suppress the immune system in order to stop the destruction of red blood cells.

Blocking of a blood vessel in the lungs by a piece that has broken away from a blood clot (known as pulmonary thromboembolism) is a risk for dogs with immune-mediated hemolytic anemia. The underlying cause is unknown, but the risk may be reduced by supportive care with fluids and blood transfusions. Fluids are important to keep kidneys functioning properly and to protect the kidneys from the high concentrations of circulating bilirubin (the reddish yellow pigments in blood that cause jaundice). If the risk for forming blood clots is high, anticoagulant medication may also be given.

Immune-mediated hemolytic anemia is a serious medical condition that causes death in 20%-75% of affected animals. The risk of death depends on which signs are seen, but rapid drops in red blood cell counts, moderate to high white blood cell counts, abnormal bruising, and excessive clotting may indicate a higher risk. Your pet's veterinarian may need to refer your dog to an internal medicine specialist.

Alloimmune hemolysis occurs when antibodies attack red blood cells of another individual of the same species. Neonatal isoerythrolysis is an example of such a disease and is seen rarely in dogs. It is caused when pups nurse from a mother whose colostrum (the yellowish fluid rich in antibodies and minerals that is produced after giving birth and before producing true milk) contains antibodies to the newborn’s red blood cells. The antibodies develop in the mother during unmatched blood transfusions. Newborns with neonatal isoerythrolysis are normal at birth but develop severe hemolytic anemia within 2 to 3 days and become weak and jaundiced. A veterinarian can perform tests to confirm the diagnosis. Treatment consists of stopping all nursing from the mother, providing nutrition through a milk replacer, and, in some cases, giving blood transfusions. If a pregnant bitch is known to have received a blood transfusion in the past, her blood should be tested against the newborn puppies’ blood before that litter is allowed to nurse.

Microangiopathic hemolysis occurs when red blood cells are damaged due to turbulent flow through abnormal blood vessels. It can be seen in dogs with severe heartworm infections, blood vessel tumors (for example, hemangiosarcoma), twisting of the spleen, and disseminated intravascular coagulation, a condition in which small blood clots develop throughout the bloodstream, blocking small blood vessels and depleting the platelets and clotting factors needed to control bleeding. Treatment requires correcting the underlying disease.

A deficiency of phosphorus in the blood, leading to destruction of red blood cells, is seen in dogs with diabetes, hepatic lipidosis (a disorder of fat metabolism in the liver), and refeeding syndrome (chemical and fluid abnormalities that occur during recovery from fasting or starvation). Providing additional phosphorus, either by mouth or by injection depending on the severity of the illness, is the recommended treatment.

Many classes of drugs can cause anemia if they are ingested accidentally or if their prescribed use is not closely monitored. These include common human and animal drugs, such as acetaminophen, aspirin, naproxen, penicillin, and many other antibiotic and antiparasitic agents. Other anemia-causing toxins include plants such as oak, red maple, and bracken fern; foods such as fava beans and onions; chemicals; and heavy metals such as copper, lead, selenium, and zinc. It is always important to give as complete a history as possible to the veterinarian when anemia is suspected, in order to help pinpoint the cause.

Many infections—caused by bacteria, viruses, or other organisms—can lead to anemia, by direct damage to red blood cells (leading to their destruction) or by effects on the elements that produce red blood cells in the bone marrow. In dogs, for example, infections involving certain organisms in the genuses Ehrlichia and Babesia are known to cause anemia.

Several inherited red blood cell disorders cause anemia. Pyruvate kinase (enzyme) deficiencies are seen in Basenjis, Beagles, West Highland White Terriers, Cairn Terriers, and other breeds. Phosphofructokinase (enzyme) deficiency occurs in English Springer Spaniels. Deficiencies in these enzymes lead to shortened red blood cell life span and a regenerative anemia. In dogs with phosphofructokinase deficiency, the sudden destruction of red blood cells is caused by a high blood pH created after excessive excitement or exercise. If such situations are minimized, these dogs may have a normal life expectancy. There is no treatment for pyruvate kinase deficiency, and affected dogs will have a shortened life span due to abnormalities of the bone marrow.

Nutritional deficiency anemias develop when the nutrients needed for red blood cell formation are not present in adequate amounts. Anemia develops gradually and may initially be regenerative, but ultimately becomes nonregenerative. Starvation causes anemia by a combination of vitamin and mineral deficiencies as well as a negative energy and protein balance. The deficiencies most likely to cause anemia are iron, copper, vitamin B₁₂, vitamin B₆, riboflavin, niacin, and vitamin E.

Iron deficiency is the most common deficiency seen in dogs. It is rarely nutritional in origin—it most commonly occurs after blood loss ( see Blood Loss Anemia). Young animals do not have much stored iron, and milk contains very little iron. Your veterinarian may recommend oral iron supplements for anemic newborns. Your veterinarian will also look for any hidden source of blood loss and treat it if needed.

B vitamin deficiencies are rare. Some drugs, such as anticonvulsants and drugs that interfere with B vitamin metabolism, may cause anemia. Poor absorption of vitamin B₁₂ has been reported in Giant Schnauzers. These dogs respond to injections of vitamin B₁₂.

Anemia caused by a longterm (chronic) disease is usually classified as mild to moderate and nonregenerative. It is the most common form of anemia seen in animals. The anemia can occur after a longterm inflammation or infection, a tumor, liver disease, or hormonal disorders such as hyper- or hypoadrenocorticism (disorders of the adrenal gland) or hypothyroidism (an underactive thyroid gland). Proteins called cytokines, which are produced by inflammatory cells, lead to decreases in iron availability, red blood cell survival, and the bone marrow’s ability to regenerate, resulting in anemia. Treatment of the underlying disease leads to correction of the anemia. There are also medications available that stimulate the production of red blood cells, but they may cause side effects.

Longterm kidney disease is a common cause of nonregenerative anemia in animals. Animals with kidney disease produce less of a kidney hormone called erythropoietin that stimulates development of red blood cells in the bone marrow, leading to anemia. A synthetic form of the hormone has been used for treatment. Animals receiving the treatment require supplemental iron to support red blood cell production.

Bone marrow disease or failure from any cause can lead to nonregenerative anemia and a reduction in the number of all types of blood cells—red, white, and platelets. With widespread marrow involvement, white blood cells are affected first, followed by platelets, and finally red blood cells.

Aplastic anemia (anemia in which the ability of bone marrow to generate all blood cells is reduced) has been reported in dogs. Most cases have no known cause, but some are caused by infections, drug therapy, toxins, or total body irradiation. The immune system may also be involved in the development of this disease. The disease is diagnosed by taking a bone marrow sample. To treat the condition, the underlying cause must be determined and eliminated. Supportive care, such as antibiotics and transfusions, and medications that suppress the immune system may also be needed. Drugs that stimulate the bone marrow can be used until the marrow recovers. If the disease has no known cause or if marrow recovery is unlikely (for example, phenylbutazone poisoning in dogs), bone marrow transplantation is helpful if a suitable donor is available. However, bone marrow transplantation may not be available in all areas.

In pure red cell aplasia, only the red blood cells or the elements that produce the red blood cells are affected. It is characterized by a nonregenerative anemia with severe reduction of the elements that produce the red blood cells in the bone marrow. It has been reported in dogs. Cases that are immune-related often respond to therapy that suppresses the immune system. Supportive treatments, such as blood transfusions, may be indicated for severe cases. A synthetic hormone that stimulates blood cell production has been reported to cause pure red cell aplasia in some dogs. Stopping the hormone treatment may eventually lead to recovery in some animals.

Primary leukemias are a type of cancer in which abnormal white blood cells replace normal blood cells. This leads to anemia and a lack of normal white blood cells and platelets. Primary leukemias are uncommon, but they have been reported in dogs. Leukemias can develop in bone marrow or the lymphatic system and are classified as acute (sudden and often severe) or chronic (long-lasting, with signs that are generally less severe). Acute leukemias, in which the marrow is filled with immature blood cells, generally respond poorly to chemotherapy. In animals that do respond, remission times are usually short. In acute lymphoblastic leukemia in dogs, the response rate to chemotherapy for the most common type of acute leukemia is about 30%, with about half the dogs surviving for at least 4 months. Other types of acute leukemia are less common and even less responsive to treatment. Chronic leukemias, in which there is greatly increased production of one blood cell line, are less likely to cause anemia and are more responsive to treatment.

Myelodysplasia (also called myelodysplastic syndrome) is a bone marrow disorder in which growth and maturation of blood-forming cells in the bone marrow is defective. This leads to nonregenerative anemia or shortages of white blood cells or platelets. It is considered a preleukemic syndrome (occurring before leukemia fully develops). Myelodysplasia occurs in dogs, cats, and humans. The disease can occur as the result of mutations in stem cells or be caused by tumors in other organs or drug therapy. Some dogs respond to treatment with synthetic hormones and steroids. Supportive care with transfusions may be helpful. Survival rates vary because myelodysplasia can progress to leukemia. Many animals with this condition are put to sleep or die of infection, bleeding, or anemia.

Myelofibrosis causes bone marrow failure after normal marrow elements are replaced with fibrous (scar) tissue. It can be the initial disease or occur as a result of cancer, immune-mediated hemolytic anemia ( see Immune-mediated Hemolytic Anemia), whole body irradiation, or hereditary anemias. Diagnosis can be made by bone marrow biopsy, a procedure that requires anesthesia. Treatment depends on the underlying cause but usually involves suppressing the immune system. Because suppressing the immune system increases the chances that your pet will catch other diseases, carefully follow your veterinarian’s recommendations for controlling exposure to disease-causing agents.