Immune mediated hemolytic anemia (IMHA) is a rare condition in cats. It is caused by a cat’s immune system attacking and destroying its own red blood cells. These cells are essential because they carry oxygen throughout the body. When the immune system destroys too many red blood cells, the body cannot get enough oxygen to function properly. Red blood cells carry oxygen around the body and therefore have a very important role to play and a deficiency in these cells can cause a range of problems. Think of it like a delivery system where many of the trucks carrying vital supplies are being destroyed by the very security system meant to protect them.

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Cats with IMHA typically show several concerning signs that develop either gradually or suddenly. Your cat may appear unusually tired or weak, showing little interest in regular activities. If IMHA occurs suddenly it can cause your cat to collapse and they may be unable to walk without assistance. Their gums will look pale, white or yellow instead of their normal pink color. Some cats will breathe more heavily than usual, even when resting, as their body tries to get more oxygen. In some cases, you might notice darker-colored urine, which can indicate that broken-down red blood cells are being passed in the urine.

Yes, there are lots of different names for anemia depending on the cause and whether it is regenerative or non-regenerative anemia. Non-regenerative means the body is not producing enough blood cells to replace those that have been lost. Bleeding (eg due to trauma) can cause a regenerative anemia. Once the blood loss is controlled, the body can create more blood cells over time. Immune mediated hemolytic anemia is also usually regenerative, the body continues to produce red blood cells, but unfortunately without treatment, the cat’s immune system will continue to attack and destroy them, leading to worsening anemia.

When you bring your cat to the veterinarian with these symptoms, they will perform several tests to confirm IMHA. The primary test is a complete blood count (CBC), which measures the number of red blood cells in your cat's blood. Your veterinarian may also run a test called packed cell volume (PCV), which is often run alongside the CBC. This is a quick test that most veterinary practices can complete in-house. The PCV will confirm anemia but it will not tell the vet the underlying cause. These tests are often used to monitor the percentage of red blood cells when the condition is first diagnosed, and then to monitor improvements once a cat has started to receive treatment. Your veterinarian will also conduct specific tests to determine if there is an underlying trigger for IMHA. Imaging and testing for infectious diseases may be performed.

In primary (non-associative) IMHA the cause remains unknown. Despite not knowing the trigger, we do know that the immune system attacks and destroys the red blood cells. Your veterinarian will usually try to rule out many conditions that can cause a secondary IMHA before confirming that it is a primary condition. Secondary (associative) IMHA is when red blood cell destruction occurs secondary to an underlying cause (eg infections, cancers or drug reactions).

Treatment for primary IMHA is complex and usually requires hospitalization, at least initially. The main approach involves using medications that suppress the overactive immune system, primarily corticosteroids like prednisone. Your cat may need blood transfusions if their red blood cell count is dangerously low. Additional medications might be prescribed to prevent blood clots, which can be a serious complication of IMHA. Treatment is typically long-term, often lasting several months, and requires careful monitoring and adjustment of medications. Secondary IMHA treatment often involves treating the underlying cause, if it is caused by a medication your veterinarian may stop the medication or advise on a withdrawal process. It is important to follow your veterinarian instructions, changing medication quickly or ignoring advice can result in deterioration or relapse. If IMHA is caused by a tumor or a serious infection, surgery and/or medical management will be advised by your veterinarian.

The recovery period for cats with IMHA varies considerably. The first few weeks are critical, and your cat will need frequent veterinary check-ups to monitor their progress. Many cats respond well to treatment, though some may experience relapses and require ongoing medication adjustments. Complete recovery can take several months, and some cats may need long-term medication to prevent recurrence.

Correct home care is crucial for cats with IMHA. You'll need to give medications exactly as prescribed, their medication is important and finding a treat to hide their medication in will be the easiest way to medicate your cat daily. Be aware that cats are clever and will start to refuse the treat if they are suspicious that there is a tablet hidden. It is worth giving them a plain treat first, followed by the treat with their medication and then a plain treat again. You can also use the selected treat during training or other opportunities so they do not become suspicious. Change the selected treat, on a regular basis. Limit your cat's activity during the early stages of recovery, as they may tire easily. Watch for any signs of weakness, pale gums, or breathing difficulties. Record their energy level, appetite and bathroom habits to share with your veterinarian. Make sure they have easy access to fresh water and a comfortable resting place. Thirst is likely to be increased as a result of the medications used to treat this disease. It is important that a cat who is suffering IMHA does not sustain an injury that will result in blood loss. As they are already anemic, any further reduction in red blood cells can be fatal. Your vet may advise that your cat does not go outside.

Contact your veterinarian immediately if you notice any of these signs: sudden weakness, collapse, difficulty breathing, loss of appetite, vomiting, or if your cat's gums become pale or yellow. These could indicate a relapse or complication that requires immediate attention. Also, call if you have any concerns about medication side-effects or if your cat seems to be getting worse instead of better. While IMHA is a serious condition that requires dedicated care and monitoring, many cats can return to normal, healthy lives with proper medical management and attentive home care.