Hemolytic Anemia in Dogs

By: Lori Teller, DVM, DABVP, CVJ

TVMA Member
Houston, TX

Published February 2017

The immune system is a beautiful thing. It keeps us healthy by stopping infectious agents before they make us ill and keeping mutated cells in check before a tumor spreads. However, sometimes the immune system goes haywire and causes problems in our bodies, which are referred to as immune-mediated problems. One of the most common immune-mediated problems is immune-mediated hemolytic anemia (IMHA), sometimes known as autoimmune hemolytic anemia. Immune-mediated hemolytic anemia may be caused by an underlying problem, such as exposure to certain medications, infectious or inflammatory agents, cancer or other triggers. Other times, the cause is unknown.

IMHA Develops When Immune System Attacks Vital Blood Cells

IMHA occurs when the immune system identifies the body’s own red blood cells (RBCs) as foreign and then attacks and destroys them. Red blood cells are responsible for carrying oxygen to organs in the body and thus are vital to all bodily functions. As the total number of RBCs decreases due to destruction, the dog develops anemia, which can become severe and life-threatening. The destroyed RBCs release hemoglobina protein in red blood cells that carries oxygen throughout the body into circulation. Hemoglobin can be toxic to the kidneys, further complicating the disease process. Clinical signs of IMHA may include pale or yellow gums (jaundice/icterus), fever, fatigue, decreased appetite, brown or orange urine, bouts of vomiting or diarrhea, blood in the stool, rapid breathing, exercise intolerance, bruising or pain.

A Range of Diagnostic Tests Are Necessary to Identify Cause

If you notice any of these clinical signs in your dog, seek veterinary care immediately. Your veterinarian will take a complete history and will need to know what medications your pet is taking, if he or she gets into the trash or eats things in the yard, if there has been exposure to fleas, tick or toxins, when it was last vaccinated, and many other facts. Your veterinarian will conduct a thorough exam and perform diagnostic tests, including bloodwork, a urinalysisanalysis of urine by physical, chemical, and microscopical means to test for the presence of disease, drugs, etc., possibly radiographs, an abdominal ultrasound or a bone marrow aspiratematter that has been drawn from the body by aspiration. Unfortunately there is not one test that is specifically diagnostic for IMHA. Veterinarians arrive at a diagnosis by evaluating the results of the history, physical exam and diagnostic tests.

Triggers Could Be The Cause of IMHA

Typically the anemia is severe, and the bloodwork may show that the body is trying to make new RBCs but can’t keep up with the pace of RBC destruction. It is important to determine if there is an underlying cause for the IMHA. If something is triggering the problem, such as a parasite, medication or tumor, removing the trigger may be necessary to resolve the IMHA and prevent a relapse. In many cases, there will not be an underlying cause. It is thought that certain breeds of dogs are more susceptible to developing IMHA, including Cocker Spaniels, poodles, basenjis, West Highland white terriers, beagles, Alaskan malamutes, Old English sheepdogs and Irish setters. Unspayed females are also at higher risk.

Treatment Involves Immune Suppression

The mainstay of treating IMHA is suppressing the immune system to stop the destruction of red blood cells. Dogs that are acutely ill often require hospitalization and may need one or more blood transfusions, in addition to supportive care such as intravenous (IV) fluids and nutritional support. A dog with IMHA may be hospitalized up to a week or even longer. The primary drugs used to suppress the immune system and control the IMHA are glucocorticoids (steroids), such as prednisone or dexamethasone, which are given at high doses. The glucocorticoids inhibit the cells of the immune system that destroy RBCs. In many cases, your veterinarian will add in a second drug to further suppress the immune system. This will help to more quickly stop the IMHA and lower the dose of glucocorticoids used, thus decreasing their side effects. Other immunosuppressants used in dogs by veterinarians may include azathioprine, cyclosporine, mycophenolate mofetil or leflunomide. In rare cases, your veterinarian may consider additional treatment options, such as splenectomy (removing your dog’s spleen), plasmaphersis (not widely available) or intravenous human immunoglobulin (which modulates activities of the immune system). If IMHA progresses beyond the need for steroids, the pet may need care by a specialist, as the other immunosuppressive drugs need much closer monitoring and 24/7 care.

Prevention of Blood Clots is Crucial

An important component of supportive care is preventing blood clots in the lungs, called pulmonary thromboembolisms (PTE). PTE are a major cause of death in patients with IMHA, and it is important to prevent their formation. There are a variety of medications that can be used, including heparin, low-dose aspirin or clopidogrel. Glucocorticoids also can be associated with an increased risk for gastric ulcers, so your veterinarian may prescribe medications to help protect the lining of your dog’s stomach.

Closely Monitor Dogs During Recovery Period

IMHA is a life-threatening disease, and mortality rates have been reported to be anywhere from 25 percent to 70 percent. The most common cause of death is lack of response to treatment, followed closely by the occurrence of PTE. It can take several weeks to months for a dog to recover from IMHA, and some dogs may need to stay on immunosuppressive drugs for the rest of their lives. Other dogs may eventually be weaned off. Dogs with primary IMHA or secondary cases in which the underlying trigger cannot be removed are prone to relapse, so it is important that any dog that has had IMHA be closely monitored for clinical signs of recurrence. It can be even more difficult to treat a patient with relapsing IMHA. IMHA is a complicated disease, and you will need to maintain close contact with your veterinarian and go in for frequent visits during your dog’s recovery period. It is rewarding for everyone to see a patient recover and lead a full and active life.

Lori Teller, DVM is a graduate of Texas A&M College of Veterinary Medicine and lives in Houston, Texas. She practices at Meyerland Animal Clinic.