Immune-Mediated Haemolytic Anaemia (IMHA)

Immune-mediated haemolytic anaemia (IMHA) is an autoimmune disease in which the immune system destroys red blood cells, causing anaemia and other complications.

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Immune-mediated haemolytic anaemia (IMHA) is an autoimmune disease that causes the immune system to attack and destroy red blood cells, leading to anaemia and symptoms such as lethargy, weakness, jaundice, and fever. Diagnosing IMHA involves blood tests and potentially other imaging tests, while treatment includes immunosuppressive medications, blood transfusions, and stroke prevention. Prognosis varies, with up to 88% survival rates reported for hospital discharge, though long-term management may be required to monitor for relapse.

What is Immune-Mediated Haemolytic Anaemia?

Immune-mediated haemolytic anaemia (IMHA) is an autoimmune disease where the immune system attacks and destroys red blood cells, leading to anaemia (low red blood cell count). Red blood cells are vital as they transport oxygen throughout the body.

IMHA primarily affects young to middle-aged dogs, with certain breeds like the American Cocker Spaniel being more prone to the condition. It is rarely diagnosed in cats. Dogs can have either non-associative IMHA (no underlying disease) or associative IMHA (caused by another disease or certain medications). Conditions linked to IMHA include cancer and infections.

What are the Signs of IMHA?

Dogs with IMHA may show signs such as lethargy, weakness, collapse, and loss of appetite. Owners may also notice yellowing of the skin, gums, or eyes (jaundice), which happens due to the buildup of bilirubin caused by the destruction of red blood cells. Urine may turn red due to the presence of haemoglobin, and dogs may have a fever, making them feel hot to the touch.

picture of a dog's mouth
A dog with yellow-coloured gums (jaundice) due to IMHA


How is IMHA Diagnosed?

To diagnose IMHA, blood samples are taken for testing. Dogs with IMHA will have anaemia and abnormal red blood cells (spherocytes) under a microscope. Red blood cells may also clump together (autoagglutination – shown in the image). A Direct Coombs Test may be done to check for an abnormal immune response against red blood cells. Elevated bilirubin levels are common on blood tests.

If associative IMHA is suspected, additional tests such as an abdominal ultrasound and chest x-rays may be recommended.

Dog blood on a slide.

What is the treatment for IMHA?

Dogs diagnosed with non-associative IMHA are treated with immunosuppressive medications, typically prednisone. Although generally well-tolerated, prednisone can increase appetite, thirst, urination, and panting and may cause secondary infections. If a dog does not respond to prednisone or has severe IMHA, other immunosuppressive drugs may be added.

Dogs with IMHA often need blood transfusions, sometimes multiple. Medications to reduce the risk of strokes may also be given, as dogs with IMHA have an increased risk. Intensive supportive care may be required for severely ill dogs.

For dogs with associative IMHA, treatment involves addressing the underlying cause along with the standard IMHA treatments.

What is the Prognosis for Dogs with IMHA?

The prognosis for dogs with IMHA is variable, with studies reporting a 50-88% survival rate to hospital discharge. In those patients who do respond to treatment, it can take up to three to five days to see an improvement. Dogs with IMHA are often on long-term medications and intermittent blood tests are required to monitor for relapse, which is reported to occur in approximately 20% of dogs. The prognosis in dogs with associative IMHA depends on the underlying cause.

The internal medicine and critical care teams at ARC are highly experienced in treating dogs with IMHA.