Red blood cells, also called RBCs, are the most common blood cell in the circulatory system. They contain hemoglobin (also spelled haemoglobin), a biomolecule containing iron, that binds to oxygen in the lungs and delivers it to the rest of the body’s cells. Once the oxygen is released, the RBC then picks up carbon dioxide and takes it back to the lungs to be expelled.
In autoimmune hemolytic anemia (AIHA), also called immune-mediated hemolytic anemia (IMHA) or idiopathic non-regenerative immune-mediated hemolytic anemia, the dog’s immune system sees the red blood cells as foreign bodies and sends antibodies to attack the RBCs. This causes them to burst, which leads to low plasma concentration levels. The components of the red blood cells get released into the surrounding blood and tissues, and this is what causes symptoms.
In very serious cases, red blood cells live only a few days instead of the normal 100-120 days. This is a very common disease in dogs. No one knows for sure why this happens, but it must be taken very seriously when a dog develops this disease.
Within the classification, there are several subtypes of IMHA. Each has different “causes” or subtypes which may result from different causes.
Primary IMHA, also called idiopathic IMHA, are caused by a primary disease. When this happens, the immune system produces antibodies to target certain antigens and proteins in the outer membrane of the red blood cells.
Secondary IMHA happens when the red blood cell membrane is damaged by infection, drug reaction, cancer, blood transfusion, exposure to toxins, or has been exposed to venom from a bite from snake, bee, or other insect. Cancer commonly causes secondary IMHA.
Intravascular IMHA occurs when red blood cells within blood vessels are destroyed by the immune system.
Extravascular IMHA occurs when red blood cells outside of blood vessels – usually within the liver and/or spleen – are destroyed by the immune system.
There is no way to prevent this disease. Aside from keeping your dog away from all medication, bees, insects, and snakes, there’s nothing you can do to prevent this disease from taking effect.
The symptoms of autoimmune hemolytic anemia are very similar to those of general anemia. They are: lack of appetite, diarrhea, pale mucous membranes, depression, lethargy, vomiting, disinterest in normal activities, fever, weakness, exercise intolerance, jaundice, bloody stool, difficulty breathing, discoloured urine, excessive thirst, elevated heart rate, excessive urination, and bounding pulse.
Dogs at Risk
Autoimmune hemolytic anemia may develop in dogs of any sex and any breed, but spayed, middle-aged dogs seem to be affected more than any other group. Specific breeds more prone to AIHA are English Springer Spaniel, Bichon Frise, Cocker Spaniel, Miniature Schnauzer, Miniature Poodle, Old English Sheepdog, Irish Setter, Finnish Spitz, Shih Tzu, Miniature Pinscher, Vizsla, Collie, Scottish Terrier, Doberman Pinscher, and Lhaso Apso. For some reason, dogs seem more likely to become affected in the spring moths of May and June. If you see symptoms in your dog, get it to a vet as soon as possible.
Testing and Diagnosis
Dogs that show symptoms of anemia are usually tested for complete blood count, a urinalysis, and have a serum biochemistry test done. One of the signs of IMHA is changes to the RBC structure, which the CBC test will show. Another test will check for red blood cell parasites like Mycoplasma hemofelis and Babesia. Other tests like a flow cytometry test, Coombs’ test, and a coagulation panel may also be helpful in determining a diagnosis of anemia. Sometimes chest x-rays may identify – or exclude – metastatic disease as the main cause. Abdominal ultrasounds can look for other cancers.
Treatment and Prognosis
Between 40 and 60 percent of all dogs with untreated autoimmune hemolytic anemia will die. Treatment must be aggressive and immediate in order to bring about a positive ending. The first goal is to correct the anemia so that the dog’s circulatory system may function properly. The second goal is to identify any disorder that may be causing the autoimmune condition that contributes to the attack on its red blood cells. While these things are being done, the dog’s health must be supported until its own red blood cell count is replenished. This may require blood transfusions in the form of packed red blood cells.
Transfusions can be dangerous, because unless the disorder is under control, the immune system will merely send more sentries to attack the new red blood cells. This can morph into an extremely aggressive immune system response that may overwhelm a weakened dog.
Drug therapies of corticosteroids like dexamethasone or prednisone might work to suppress the dog’s immune system. This works to slow down or halt the attack on its RBCs and/or the red blood cells from a transfusion. Stronger drugs like cyclophosphamide or azathioprine (chemotherapy drugs) might be used if corticosteroids do not work. These, of course, bring with them adverse side-effects and these drugs should be avoided as a first option.
When a dog’s autoimmune hemolytic anemia is treated immediately and aggressively, its chances for a positive outcome are fairly high; however, many dogs will experience a relapse later in life. The underlying cause of the condition will alter the dog’s prognosis.