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IMHA (Immune Mediated Haemolytic Anaemia) Fact Sheet

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What is Immune Mediated Haemolytic Anaemia (IMHA)? 

IMHA is a disease where the body’s immune system destroys its own red blood cells. This often leads to severe anaemia and poor oxygen delivery to multiple organs such as the kidneys, liver, brain, etc. Both dogs and cats are affected by this condition.

What are the signs of IMHA in cats and dogs?

The signs that a patient shows vary depending on the severity of the disease. Some dogs and cats suffer acute severe disease and can present collapsed and unable to stand. Their gums are often very pale and you may also notice a yellow tinge in their eyes, mouth or skin. This is due to staining of the mucous membranes or skin with bilirubin which gets released into the circulation when large numbers of red blood cells are destroyed. The patient may be breathing fast due to either the anaemia, or the formation of blood clots in the lungs, which is a common complication in patients with IMHA. Sometimes the disease is not as severe and the signs may be milder (e.g. lethargy).

What are the causes of IMHA in cats and dogs?

IMHA in dogs and cats can be triggered by different factors including infectious organisms, tumours and even drugs. It is therefore extremely important to inform your vet of any medication that your pet has recently received. Investigations will then be recommended to make sure that there is not an underlying disease present. When a cause is not found, the disease is designated idiopathic (aka primary) IMHA; this means that without an obvious underlying trigger, your pet’s immune system has started destroying its own red blood cells.

How is IMHA diagnosed?

A diagnosis of IMHA in dogs and cats can often be made based on the clinical signs, blood tests and examination of a blood smear. Other tests should then be performed to differentiate primary IMHA from that triggered by other diseases (tumours, infections, etc). This is extremely important as the treatment of these conditions is often very different to that of primary IMHA. An incorrect diagnosis could lead to poor treatment response and even death. Additional tests which may be carried out include X-rays, abdominal ultrasound, serological tests to check for infectious organisms or, occasionally, bone marrow biopsies.

What treatments are available for IMHA?

If an underlying disease is present, this should be treated, since successful treatment of the underlying trigger often leads to resolution of IMHA. In cases of idiopathic or primary IMHA in dogs and cats (where a clear cause is not present), steroids are given to suppress the immune system. Other drugs such as azathioprine or ciclosporin are sometimes used in conjunction with steroids, particularly in difficult or severe cases (or as alternative sole treatment if steroids are not well tolerated). Some pets will require blood transfusions to replace red blood cells, however, the benefits are sometimes short-lived as the transfused red blood cells may also be destroyed by the immune system (hence the requirement to combine with immunosuppressive therapy). Your vet may also advise using heparin or anti-platelet drugs to prevent the risk of clot formation.

What is the prognosis for pets diagnosed with IMHA?

The prognosis for IMHA in dogs and cats is very variable and depends on the severity of the disease and the presence of an underlying cause. In recent years there has been some research into new drugs and massive improvement in the care and monitoring of these patients. However, despite all efforts, sadly some patients succumb to the disease. The main risk of death is within the first few days/weeks of treatment. The prognosis for dogs and cats that respond to treatment and are discharged from hospital is generally good although some may require long term treatment.


If you are concerned about the health of your pet you should contact your veterinary surgeon.

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