Anemia Related to the Immune System in Dogs

Anemia occurs when red blood cell counts drop below a normal level. This can happen either through blood cells loss, or lack of production. Anemia that is the result of red blood cell destruction is called hemolytic anemia. There are many ways in which red blood cells can be lost, including trauma, chronic bleeding, infection and toxin ingestion. Sometimes however red blood cells can be destroyed by a dog’s own antibodies when the immune system fails to recognize the cell and attacks it as if it were an infectious threat. This type of anemia is called immune-mediated hemolytic anemia (IMHA). This process happens naturally to some extent, as old or infected blood cells are marked with antibodies and recycled by the spleen, but in IMHA the process has swung out of control and large numbers of healthy cells are destroyed. The disease may develop slowly, or it may start with a sudden life-threatening attack. Dogs with severe IMHA are also at risk for developing pulmonary thromboembolism since the antibody surrounded red blood cells tend to stick together and are more likely to form a clot. Most conditions will respond to treatment, but serious attacks can end still up being fatal. Mortality rates vary widely, from 20-75%, depending on the severity of the symptoms.

When antibodies from the immune system attack and destroy a dog’s own red blood cells, anemia can result. This type of anemia is defined by veterinarians as immune-mediated hemolytic anemia. Mild conditions can be treated, but severe attacks are often fatal.

Vomiting and diarrhea are commonly the first symptoms of IMHA rather than the more traditional signs of anemia. Have your dog evaluated for any of the following signs:

• Vomiting
• Diarrhea
• Fever
• Poor Appetite
• Weight Loss
• Lethargy
• Lack of stamina
• Weakness
• Rapid heart rate (tachycardia)
• Rapid breathing (tachypnea)
• Paleness of mucus membranes, especially notable around the gums
• Blood in the stool
• Jaundiced, yellowish appearance
• Dark urine

Types

There are two basic types of anemia. 

• Regenerative anemia – an anemic condition in which the bone marrow continues to generate new red blood cells. Almost all cases of IMHA fall into this category since the bone marrow is not involved and will still produce new cells.
• Non-regenerative anemia – conditions in which the bone marrow fails to generate new red blood cells. Occasionally, a very severe autoimmune response can target the blood stem cells in the bone marrow and lead to non-regenerative IMHA.

Cases of IMHA fall are also divided into two types based on how they develop.

• Primary – the autoimmune response develops on its own with no obvious trigger.
• Secondary – the autoimmune response develops secondary to another factor.

Primary conditions are more common and the cause is basically unknown.

• Idiopathic – 60-75% of the cases of IMHA in dogs fall into this category
• Hereditary – this is believed to play a role, but it’s not known specifically what gene or genes are responsible. These breeds have shown a higher incidence, but IMHA could develop in any dog.
• Cocker Spaniels (higher prevalence in most studies)
• Miniature schnauzers
• Poodles, Irish Settlers
• Old English Sheepdogs
• Female dogs more likely to develop the problem

Conditions which can trigger IMHA as a secondary response include:

• Cancer tumors (especially hemangiosarcoma, a tumor of the spleen)
• Some drugs (including types of penicillin, trimethoprim-sulfa, and methimazole)
• Infections (including mycoplasmosis and babesiosis)
• Vaccinations
• Bee sting venom

A blood test with a complete blood cell count will show that your dog has anemia. Veterinarians can sometimes tell if the anemia is regenerative by noting different stages of maturity among the cells, as well as corresponding high levels of white blood cells and platelets. The veterinarian will check for signs of external or internal bleeding which could produce the similar blood test results to regenerative IMHA.

Several other factors can specifically indicate IMHA. Jaundice with regenerative anemia is one sign, as well as the presence of spherocytosis, abnormally spherical shaped blood cells, on a blood smear test. In severe cases, the stickiness of the red blood cells will be noticed on blood examination also. Another blood test, called a Coombs test, can help to determine if antibodies are attacking the red blood cells.

The veterinarian will try to eliminate infectious causes of hemolytic anemia as much as possible. In the presence of an infection, antibodies can sometimes behave in a similar way to IMHA. Any immune suppressant treatment will limit the dog’s power to fight infection, so this can be an important step. The veterinarian will need your dog’s complete medical history, and recent medications which could have triggered the condition, as well as a detailed description of the nature and onset of symptoms.

Very severe cases will need immediate blood transfusions to reduce coagulation and increase healthy blood cells levels. In severe crises, very fast acting immune suppressant medication is prescribed, such as cyclosporine or human intravenous immunoglobulin. These types of medications will only be used in cases requiring immediate action to save your dog’s life.

In milder, slower developing cases a traditional immune suppressant medication such as prednisone or corticosteroids is often effective. Daily aspirin is sometimes prescribed also. The veterinarian may try several medications depending on how your dog responds to treatment.

If an underlying infection is found, the veterinarian will prescribe an antibiotic to treat it, as well as stabilizing the blood with transfusion if necessary. Antibiotics may also be given to compensate for strong immune suppressants which limit the body’s ability to fight infection.

Recovery from mild symptoms is likely, as long as your dog responds to immune suppressant therapy. Recovery from severe, sudden attacks is less common, but it is possible as long as your dog gets immediate treatment and is able to survive the first crisis. Immune suppressant medication may need to continue for some time, especially if the cause is unknown. You should monitor your dog closely for infection while taking this kind of medication, as the natural antibodies will not be as effective. If a triggering factor is found, once the episode is past your dog may not have further problems. Regular check-ups and blood tests would still be advisable however.