Immune mediated hemolytic anemia (IMHA) occurs when a patient’s own immune system starts to attack the body’s red blood cells (RBCs). When too many red blood cells are destroyed, the patient develops an abnormally low red blood cell count, also called anemia. The primary function of the red blood cell is to transport oxygen to the tissues, and when this oxygen transport decreases to a critical level, clinical signs occur. IMHA can be primary (no known cause) or can be secondary to a detectable cause such as infections, drug reactions, blood parasites, cancer, and inherited red blood cell defects.
Immune mediated hemolytic anemia is diagnosed much more commonly in dogs than in cats. Female dogs are more commonly affected. Certain breeds of dogs are predisposed including Cocker Spaniels, Poodles, West Highland White Terriers, Springer Spaniels, Old English Sheepdogs, Schnauzers, and Irish Setters. In cats, IMHA is often associated with certain underlying infections including feline leukemia virus and red blood cell infections.
Signs & Symptoms
Clinical signs depend on the severity of the anemia and the underlying cause. Symptoms can range from mild and vague to severe and life threatening including:
- Decreased appetite
- Labored breathing
- Pale gums
- Increased heart rate
- Jaundice (yellow gums and/or skin and eyes)
- Weight loss
- Pica (eating abnormal items such as dirt)
- Dark red or brown urine
Physical examination by a veterinarian may also detect a heart murmur and an enlarged spleen. Mild symptoms can quickly progress to severe life threatening signs. Collapse, unconsciousness, or even death can occur if the anemia is severe.
A complete history and thorough physical examination by a veterinarian are the first steps in arriving at a diagnosis of IMHA. Your veterinarian will ask you questions regarding your pet’s medical history including when the signs were first noticed, what kind of symptoms you have seen, recent medications or vaccinations, and recent travel. Anemia is suspected when the oral mucous membranes (gums and tongue) are pale or white. Anemia is confirmed by performing a standard blood test that measures the red blood cell (RBC) count or the packed cell volume (PCV). Following a diagnosis of anemia, additional testing may be recommended to determine the underlying cause of the anemia including evaluation for an immune cause. Since there are many potential causes for anemia, more specific testing is often necessary.
Laboratory testing is also useful to determine whether new red blood cells are being produced, to evaluate the function of the body’s other organs, and to search for underlying causes (like infections or cancer). X-rays and ultrasound may be recommended to search for underlying tumors and to further evaluate the internal organs.
Treatment & Aftercare
Focus is placed on three main goals of therapy:
- Stabilizing the patient
- Treating any underlying cause for the IMHA if detected
- Suppressing the immune system in order to stop the immune attack on the red blood cells
Hospitalization, possibly with intensive care and red blood cell transfusions, may be necessary depending on the severity of the disease process. Supplemental oxygen therapy may be necessary. Your veterinarian may discuss discontinuing any recent medications which could trigger IMHA. If an infection is suspected, an appropriate medication for the infection will be given. High doses of steroid medications (such as prednisone or dexamethasone) are commonly given to help control the immune attack on the red blood cells. Additional immunosuppressive drugs may also be needed, especially in more severe cases. Because the red blood cell destruction can result in blood clots, anticoagulant drugs like aspirin may be needed. Newer advanced treatments like blood purification are being investigated and are sometimes recommended in severe cases.
Once immunosuppressive therapy is started, response to treatment is expected within 1 to7 days if the medications are effective. Additional medications are often added if an adequate response is not seen. The patient is placed on oral medications when tolerated, and these medications are typically given daily for at least several months. The medication doses are slowly lowered by your veterinarian based on recheck examinations and lab tests. Rapid tapering of the medications may be more likely to result in relapse. Unfortunately, relapses of this disease can occur even in patients that are well controlled.
IMHA is a serious disease and mortality rates (the percentage of animals who either die or are euthanized as a consequence of this disease) in the range of 20-80% have been reported. For patients that respond quickly to immunosuppressive therapy and do not need repeated transfusions, prognosis can be good. Patients that require repeated transfusions or quickly destroy transfused red blood cells have a much poorer prognosis. Mortality rates increase dramatically if complications including blood clots occur.
Fact Sheet Author:
Carolyn Briggs, DVM, Diplomate ACVIM (SAIM)