Hemolytic anemia is a rapidly life-threatening condition. Many of the causes of red blood cell destruction progress quickly. After oxygen is inhaled into the lungs during breathing, it is transferred from the air to the red blood cells. These red cells then carry the oxygen through out the body to all the tissues. Because red blood cells carry oxygen to the tissues, when red cells are depleted the body is basically starved for oxygen.
In addition to oxygen starvation, the destruction of the red cells (hemolysis) releases products from inside of the cells. In large quantities, these products cause some of the signs associated with hemolytic anemia, like jaundiced gums and eyes and discolored urine, which can cause damage to the pet.
There are many causes of anemia other than hemolytic anemia. For instance, an animal may become anemic due to bleeding, or may become anemic when the body makes insufficient quantities of new red blood cells.
Appropriate treatment depends on an accurate diagnosis as to cause. The success rate for the treatment of hemolytic anemia depends on the cause. Some types respond very well to treatment, while others respond poorly even with appropriate treatment.
Causes of Hemolytic Anemia in Dogs
As mentioned, there are many causes of anemia. The veterinarian’s first task after identifying anemia is to determine if the cause is blood loss, insufficient production of blood cells, or hemolysis. Hemolytic anemia refers specifically to those causes of anemia which are due to destruction of the red blood cells. Bleeding is a common cause of anemia, which is not related to hemolysis. For instance, an animal that has bleeding stomach ulcers may be anemic, but it is not hemolytic anemia. Another type of anemia is due to insufficient production of red blood cells. Red blood cells are made in the bone marrow, or the soft red center of the bones. Decreased production of red cells may be caused by either disease inside the marrow such as cancer in the marrow, or by disease outside the marrow. For example, animals in kidney failure don’t send normal signals to the marrow that it should make more red cells. The most common cause is a disease known as immune mediated hemolytic anemia (IMHA). In this disease, the body’s immune system, which is designed to kill germs, instead begins to kill the animal’s own red blood cells. This disease occurs far more commonly in dogs than cats. It typically affects young to middle aged animals, with females affected more often than males. Certain dog breeds, including cocker spaniels, poodles, and Old English sheepdogs, are affected more often than other breeds. Some types of germs and parasites infect the red blood cells directly. These infections can result in destruction of the red cells. Some of these affect dogs more often than cats (Babesiosis), while others are far more likely to affect cats than dogs (for instance, Haemobartonellosis). Certain toxins can also cause destruction of red cells. These include drugs (like Tylenol, especially in cats), foods (like onions), and metals (like zinc, which is found in a surprising number of common items, including pennies and diaper rash ointments). When a very young puppy develops hemolytic anemia, it is more likely to be due to the ingestion of a toxin than to an immune mediated cause. Recently, there have been reported cases of anemia caused by skunk spray. The alkyl mercaptans and disulfides in skunk spray can cause oxidative damage to the red cells causing heinz-body hemolytic anemia in some dogs. Mechanical damage to the red blood cells can also result in their destruction. This can occur as a result of the cells being passed through twisted or damaged blood vessels. Examples include a severe and unusual form of heartworm infection, or a twisted spleen (splenic torsion). There are hereditary diseases in which the red blood cells do not work normally, and these conditions may lead to premature destruction of the abnormal red blood cells. These diseases are most often identified in purebred dogs, and the signs are usually not seen until the animals are young adults.
Some diagnostic tests are considered essential to the evaluation of hemolytic anemia. Other tests may be essential to an individual animal, as indicated by the results of the animal’s history, the physical examination, or preliminary test results. Expect the following to be performed in all cases of hemolytic anemia. Your veterinarian will begin by asking detailed questions about what you have noticed that is out of the ordinary, and when these changes began. Also expect questions about your pet’s diet, elimination habits and the color of the stool and urine, any medications, including herbal supplements, your pet may be receiving, and when the most recent vaccinations were given. Your veterinarian will complete a physical examination. This will include looking for evidence of bleeding, evaluating gum and eye color (pale gums are found in all types of anemia, but a jaundiced appearance suggests hemolysis), listening to the heart and lungs, and palpating for swellings or organ enlargement. A complete blood count (CBC) includes both a count of the various blood cell types, and an evaluation of the shape and size of the blood cells. It may also show parasites infecting the red cells. A packed cell volume (PCV), or hematocrit, is a simple measure of red blood cells. Although a complete blood count will be necessary, because a PCV is a very quick, simple, inexpensive test, it is often performed while waiting for the CBC, or to follow changes in the red cell count on a daily basis. A serum biochemical profile will be performed to evaluate organ function and the balance of salts in the body. This simple blood test may provide clues about the cause of anemia. A urinalysis detects byproducts of red blood cell breakdown in the urine, as well as assessing kidney function.
The following tests are indicated in many, but not all, cases identified as having a hemolytic anemia. A Coombs test uses a small amount of the animal’s blood to look for evidence that the immune system is causing the red cell destruction. Antibodies are normally produced by the immune system to attach to and destroy germs. For unknown reasons, sometimes the immune system begins to make antibodies that attach to the red blood cells instead of germs. The Coombs test looks for antibodies attached to red blood cells, and is particularly useful in the diagnosis of immune mediated hemolytic anemia (IMHA). Antinuclear antibody (ANA) tests may be performed to look for further evidence of a misdirected immune system. A disease called systemic lupus erythematosus (SLE) is one cause of this misdirection, and an ANA test helps in the diagnosis of SLE, but does not specifically test for IMHA. Radiographs (X-rays) may be taken to look for evidence of metallic objects like pennies in the animal’s stomach, or for evidence of enlarged or twisted organs. In addition, cancer sometimes triggers the immune system to destroy red blood cells, so radiographs may prove useful in looking for evidence of cancer in the animal’s chest or abdomen. Ultrasound utilizes sound waves to form a picture of the internal organs. This test may be used in certain settings to determine the cause of hemolytic anemia. For instance, and ultrasound picture of the spleen may show twisted blood vessels, or an ultrasound picture of the heart may show a mass of heartworms stuck together blocking the flow of blood into the heart. This test may require referral to a specialist. Specific tests may be indicated to look for infections of the blood. These usually involve submitting a blood sample to a special laboratory. Blood parasites are often visible under a microscope, but not always. Special blood tests may be needed to identify some of the hidden germs or parasites. Other tests may be indicated in a given pet. For instance, a genetic test may be used in a young, purebred dog suspected to have a hereditary cause for hemolytic anemia.
One or more of the diagnostic tests described above may be recommended by your veterinarian. In the meantime, treatment of the symptoms might be needed, especially if the problem is severe. The following nonspecific (symptomatic) treatments may be applicable to some, but not all pets with hemolytic anemia. These treatments may reduce severity of symptoms or provide relief for your pet. However, nonspecific therapy is not a substitute for definite treatment of the underlying disease responsible for your pet’s condition. Blood transfusions may prove life saving. Either fresh blood or a concentrate of red blood cells may be administered through an intravenous catheter. This transfused blood enables oxygen to be delivered to the tissues. Unfortunately, without stopping the cause of hemolysis, the newly transfused cells will themselves be destroyed. Artificial blood products may be used in place of real blood transfusions. These are not completely man-made, but are derived from components of cow blood. Because immune system destruction of the blood is the most common cause of hemolytic anemia, animals will often be treated with corticosteroids to suppress the immune system. Corticosteroids, such as prednisone, are intended to slow down the immune system’s attack on the cells. Treatment of immune mediated hemolytic anemia (IMHA) may require additional immunosuppressive drugs in order to control destruction of the cells. Intravenous fluids may be indicated, whether or not the animal receives a blood transfusion. This can support the animal during other treatments, and lessen the likelihood of complications from hemolysis. Other treatments depend on the correct identification of the cause for hemolysis. For instance, if small, coin-shaped pieces of metal are seen in the stomach on x-rays, these will need to be removed either with an endoscope (a fiberoptic tube passed through the mouth into the stomach) or via surgery. Infectious causes of hemolytic anemia may respond to drug therapy.