Immune-Mediated Hemolytic Anemia

Causes of IMHA in Dogs vs. Cats

In dogs, about 75% of IMHA cases have no known trigger or cause. In cats, most cases of IMHA have an event that can explain why the IMHA developed.

Causes of secondary IMHA in dogs include infections with tick-borne diseases, whipworm infections, heartworm disease, leptospirosis infections, and Leishmania infections.

Causes of secondary IMHA in cats include FIV infections, Feline leukemia infections, FIP, and Cytauxzoon felis infections.

Various types of cancers and inflammatory disorders can cause IMHA in both dogs and cats.

Certain drug administration can cause secondary IMHA. Drugs that have been associated with IMHA are safe in the majority of the pet population and there is no test to run to determine which pets will have these severe reactions. Drugs include carprofen, cephalosporins, methimazole, griseofulvin, penicillins, TMPS, and levamisole.

Vaccines have been implicated as a cause of IMHA, but this has not been proven.

Symptoms of Immune-Mediated Hemolytic Anemia in Pets

Clinical symptoms can vary widely and most pets only display a few of these symptoms.

• Lethargy
• Weakness
• Collapse
• Reduced appetite
• Depression
• Brown or red urine
• Black or red stools
• Pale gum color
• Yellow discoloration to the skin (more common in dogs than cats)
• Panting/increased breathing rate
• Nose bleeds
• Red dots on skin or gums (petechiation)
• Rapid heart rate

What Tests Are Available For IMHA?

The most common starting test is blood work, including a CBC, to evaluate the red blood cell count. Most pets with IMHA will be anemic (low red blood cells) and are producing a lot of new red blood cells to try to compensate. This is called regenerative anemia. Dogs will often have an increase in their white blood cell levels, but cats do not follow this trend. Some pets will also have low platelets. Pets with immune-mediated destruction of their red cells and platelets have a condition called Evan’s Syndrome.

A blood smear and saline agglutination tests are likely the next steps if the CBC is suggestive of IMHA. If the saline agglutination test shows a specific cluster of red blood cells, your pet has IMHA. A Coomb’s test or flow cytometry may be needed if the saline agglutination test was not diagnostic.

If your pet has severe anemia that is non-regenerative (not producing new red cells), your pet may need a bone marrow biopsy to see if there is another reason for the anemia. Cats should also be tested for FeLV and FIV.

My pet has been diagnosed with IMHA. What are the potential treatment options?

Many pets with IMHA have such severe anemia that they need a blood transfusion to feel better faster. The transfused red blood cells only last for a limited amount of time and are not a cure, but they will make your pet feel much better as the immunosuppressive medications start to take effect.

Immunosuppressive drugs are the mainstay of IMHA treatment. Steroids, such as prednisone/prednisolone and dexamethasone, are the most common drugs to start treatment with. Azathioprine and cyclosporine are immunosuppressive medications that may be used in addition to steroids.

The immunosuppressive medications are given for months, and the blood work is rechecked every 2 weeks or so to be sure the anemia is improving, and the body is tolerating the drugs. Once the red blood cell level returns to normal for over a month, your vet will likely start to slowly reduce the dose of the medications. Dose reductions are often done every 2-4 weeks if the blood work remains normal. If the anemia starts to develop again, the drugs are increased, and your pet may need to stay on immunosuppressive medications for a long time. Fortunately, most pets can eventually stop the medications.

Blood clots commonly develop in dogs with IMHA, so antithrombotic medications are often started. Clopidogrel, heparin, and ultra-low dose aspirin are the most common options.

Read more:

Vaccine Reactions in Dogs and Cats

Why is my cat not eating? 3 Common Causes of Anorexia in Cats

Warning Signs of Cancer in Dogs

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