IMHA is the easier-to-say abbreviation of “Immune Mediated Hemolytic Anaemia”. The condition was previously known as “autoimmune hemolytic anaemia” or AIHA, which is equally difficult to say.
IMHA is a severe form of anaemia in dogs. Just like other types of anaemia, it means something has reduced the circulation of red blood cells or haemoglobin in your dog’s body. Because red blood cells are what carry oxygen and energy around the body, anaemia can make your dog very sick, very quickly.
As well as being a form of anaemia, IMHA is also the most common autoimmune disease to affect dogs. However, it isn’t a very common condition, so many owners don’t know what IMHA in dogs is. So, in this guide we’ll tell you all about the signs and symptoms of IMHA, how it’s diagnosed and treated, and what the outlook is like if your dog is diagnosed with this condition.
Anaemia is a condition where a dog’s body has less haemoglobin and red blood cells than normal, or their red blood cell circulation is reduced. There are a number of different types of anaemia, and they are all usually a symptom of another illness.
IMHA is a severe but relatively common form of anaemia in dogs. It’s also an autoimmune or “immune-mediated” disease, as described by the first half of its long name.
Like any autoimmune or immune-mediated condition, IMHA is caused by a problem with your dog’s immune system, which makes it overreact and harm your dog’s own cells rather than harmful foreign cells.
In a healthy dog’s body, the immune system will usually identify and destroy any harmful bacteria and other pathogens that have invaded their body. It defends your dog against anything that shouldn’t be there.
However, for a dog with IMHA, their immune system mistakenly identifies their own red blood cells as harmful and destroys them instead.
Their body will still make new red blood cells in their bone marrow, but their immune system will be destroying these cells much quicker than it should be, causing anaemia. This means the circulation of oxygen and energy within the body is reduced, and carbon dioxide isn’t removed as quickly as it should be.
Hemolytic anaemia in dogs also causes their red blood cells to stick together and for their blood to clot abnormally. This means dogs with IMHA are at greater risk of thrombosis.
There are two types of IMHA, primary IMHA or secondary IMHA.
Primary IMHA means that there is no known trigger that has caused the disease. Instead, a fault in the dog’s immune system itself has caused it to attack their red blood cells. Primary IMHA is sometimes known as idiopathic IMHA, because there is no identifiable cause for their faulty immune response. The primary cause is their immune system itself.
Meanwhile, secondary IMHA is when your dog is sick or poisoned, which can result in them developing IMHA. As there’s an underlying trigger, their IMHA is secondary, because it’s a result of something else happening within their body.
Thankfully, IMHA in dogs is not considered contagious. If your dog is sick, they won’t pass it on to another dog or human in their household.
Although cats can also develop IMHA, they can’t catch it from other cats or dogs, and vice versa.
Sadly, IMHA in dogs can be fatal. However, the sooner your dog is diagnosed and treated, the better their chances of survival.
Additionally, modern advances in veterinary medicines and new treatment options being developed means that your dog has a greater chance of surviving IMHA compared to dogs from a few years ago.
However, the mortality rate for IMHA in dogs is still stubbornly high. Figures vary, with studies indicating anything between a 30% and 70% mortality rate in dogs. However, current estimates put the mortality rate at 50%, and most deaths occur within two weeks of your dog showing signs of illness.
If a dog survives the first two weeks after symptoms emerging, and receives appropriate veterinary treatment, it’s likely they will recover. So, if your dog shows any signs of illness, you must take them to the vet right away.
Cases of secondary IMHA will be triggered by an underlying illness, infection, or toxin in your dog’s system. These triggers could be anything ranging from cancer, bee stings, tick-borne infections, viral or bacterial infection such as leptospirosis, eating a toxic plant, or ingesting human medicine or other drugs.
These triggers can cause a change to the cells in your dog’s body, so their immune system starts to wrongly identify red blood cells as antigens that need to be destroyed.
However, these triggers don’t necessarily cause IMHA, but they’re associated with it. More research is needed to understand the effect of environmental factors and the development of IMHA in dogs.
In the case of primary IMHA, there is a fault with the dog’s immune system itself which causes it to attack their red blood cells. Primary IMHA is also known as idiopathic IMHA, because there is no identifiable cause for the dog’s overactive immune response.
There is a link between genetics and IMHA because certain breeds seem to be more prone to developing the condition. However, more research is needed to understand this, as current studies cannot conclude what this link could actually be.
Furthermore, the breeds typically affected by IMHA vary according to their geographical location, so the causes of IMHA are complex and could be a combination of genetics and environmental factors.
IMHA can affect any dog of any age or breed. However, it tends to be diagnosed in middle-aged dogs. Female dogs are also at greater risk of developing IMHA compared to male dogs.
Neutered dogs also make up a number of IMHA patients, but there is currently no link between neutering and raised IMHA risk. It could be that neutered dogs simply make up a big proportion of the dogs being treated because neutered dogs make up a large proportion of the doggy population.
Certain breeds of dog have a greater risk of developing IMHA compared to other dog breeds and the average doggy population. The breeds linked to a greater risk of IMHA include:
American Cocker Spaniels
Old English Sheepdogs
The signs of IMHA in dogs will vary depending on the severity of your dog’s condition. Some dogs might show milder signs of illness like lethargy, loss of appetite, and pale gums. Meanwhile, severe cases will present more worrying symptoms such as bloody urine and collapse.
One of the first symptoms of any type of anaemia is weakness and lethargy. This is because your dog’s red blood cells normally carry oxygen and energy to every inch of their body so they can move, play, and survive. However, the presence of anaemia means their red blood cells are being destroyed or damaged, so they aren’t getting enough energy and oxygen around their body.
Pale gums are also a common sign of anaemia in dogs, including IMHA. This is because a healthy dog’s gums are made a bright pink colour by the circulation of red blood cells through the tissue. But an anaemic dog has fewer red blood cells going round so their gums go pale. If your dog has IMHA, their gums might even develop a yellow tinge almost as if they are jaundiced.
If a dog has IMHA, the whites of their eyes might also go yellow. This is because when red blood cells break down, the liver removes the iron to recycle elsewhere in the body. The iron leaves a yellow pigment called bilirubin. With the normal breakdown of blood cells in a healthy dog, bilirubin is removed by the liver and excreted when a dog goes to the toilet.
However, when a dog has IMHA, their liver becomes overwhelmed as the red blood cells are destroyed faster than the liver can remove them. Therefore, bilirubin builds up in their body and turns some of your dog’s tissues yellow, including their gums and the whites of their eyes.
Pale or yellow gums
Yellow eyes and skin
Increased breathing rate
Increased heart rate
Discoloured urine (red or black)
If your dog is showing any signs of IMHA you must take them to your vet as soon as possible. IMHA is a life-threatening illness, but the sooner a dog is treated, the better their chances of survival.
Sadly, it’s difficult to prevent IMHA in dogs because so many cases are idiopathic and have no identifiable cause. Because it happens seemingly at random and is often a direct fault within a dog’s immune system, there’s little you or your vet can do to prevent it from happening.
However, keeping your dog as healthy as possible might help to prevent some of the triggers for secondary IMHA. You can keep your dog in good overall health by providing them with a healthy diet, regular exercise, routine antiparasitic treatment, and regular grooming.
Firstly, your vet will give your dog a thorough physical examination and talk to you about their symptoms, their medical history, and lifestyle. This will help them to build a picture about your dog’s health and what factors could be causing their illness.
If your vet suspects your dog has IMHA, they will conduct a blood test. They may carry out a blood smear, which is where they examine a small sample of your dog’s blood under a microscope. During this examination they will be looking for spherocytes, which are red blood cells which are smaller, denser and rounder than normal red blood cells. The presence of spherocytes is a strong indicator of hemolytic anaemia.
When your vet takes blood for testing, they might notice the blood clumps and clots together and separates from the plasma. This is called agglutination and it’s common in dogs with IMHA.
As well as a smear, your vet might conduct a complete blood count to test how many cells are in your dog’s blood. They will examine your dog’s “packed cell volume” to determine how many red blood cells they have. In a healthy dog, 35-55% of their blood will be made of red blood cells. Anything less than 35% indicates your dog is anaemic.
However, there are a number of different types of anaemia, with different causes, so your vet might conduct further tests to eliminate other possible illnesses before they can diagnose IMHA.
As well as blood tests, your vet could conduct a Coombs test, which detects antibodies against the red blood cells. Up to 75% of dogs with IMHA will have a positive Coombs test.
Finally, your vet might carry out other tests such as x-rays or ultrasounds to look for any underlying illnesses, such as cancer, which might have triggered IMHA in your dog. These tests will also help your vet to determine whether your dog is suffering from primary or secondary IMHA and determine what treatment your pup will need.
There is no cure for IMHA in dogs, and all treatment will be supportive to manage your dog’s symptoms and to limit their immune response so it stops destroying their red blood cells.
Here are all the things your vet might do to help your dog, but not every dog needs all of the treatments on this list.
If your dog is suffering from severe anaemia they may require a blood transfusion. Just like a human blood transfusion, a sample of your dog’s blood will be compared with donor blood to find a match. (Yes, dogs can donate blood too!)
This donated blood will be given to your dog via an intravenous line, like a drip. This introduces some healthy red blood cells into their body which should help to stabilise them, so their life is not in immediate risk.
Having some healthy blood will also help to alleviate their symptoms and make them strong enough to receive further treatment. Not all dogs will need a blood transfusion, while others may require several.
Because IMHA is caused by the immune system attacking and destroying your dog’s own blood cells, their immune system will need to be suppressed for a short period of time to give their body the chance to stabilise and for their number of red blood cells to return to normal.
In most cases of IMHA in dogs, the dog will be given glucocorticoids (steroids) to suppress their immune response and to reduce inflammation.
Alternatively, your dog may be given specific immunosuppressant medication, a bit like the medicine used after an organ transplant. There are different kinds of medicines used, but azathioprine or cyclosporine are two of the most common.
Your dog will probably need to take a tablet once or twice a day for around 3-6 months until their immune system is brought under control and they recover from the symptoms of their anaemia. Once your vet is happy with your dog’s recovery, they will gradually wean your dog off of their medication to prevent side-effects and to avoid suppressing their immune system for longer than necessary.
A small number of dogs may suffer a relapse. If this occurs while they are being weaned off of their medication, the dosage of their medication will just be increased again until they improve. However, if it occurs after they have completed their initial treatment, they may need to repeat the treatment with a slower process to taper them off of their medication this time.
Because IMHA in dogs causes the blood to clot abnormally, your vet might give your dog a prescription of blood thinners to prevent thrombosis and blood clots. Ultra low-dose aspirin has also proven effective at helping to prevent thrombosis in dogs.
If your dog has developed secondary IMHA, they might need medication or surgery to treat the underlying illness, infection, or toxicity which triggered their anaemia. Your vet will provide appropriate treatment for whatever is causing their illness.
It’s important to stress that there are no home remedies that will cure IMHA in dogs. In addition, this condition is life-threatening and requires hospitalisation and aggressive treatment to give your dog the best chance of survival.
However, once your dog has recovered from IMHA and is in remission, there are some natural supplements you could use that might help to protect their health and prevent secondary blood clotting or a recurrence of their IMHA.
Omega-3 is one natural product you could give your dog either in their diet or as a supplement to try and prevent clotting or IMHA relapse. This is because omega-3 has proven anti-inflammatory and anti-clotting properties. Omega-3 may also have an immune-modulating effect, meaning it can help to moderate an overactive immune response.
Meanwhile, Vitamin E is proven to inhibit the blood’s ability to clot. In a healthy dog, too much vitamin E can lead to thinner than normal blood. But for a dog with IMHA, a small amount of vitamin E as advised by your vet might help to prevent abnormal clotting.
Finally, the flavonol quercetin (which is naturally found in a number of fruits and vegetables) appears to have some anti-inflammatory effects. It is sometimes given to dogs with allergies to reduce their inflammation and to modulate their immune response. There is a possibility it could also be effective for some dogs with IMHA.
Remember you must ask your vet for advice about any supplements you plan to give your dog. Even natural supplements may not be safe for dogs with underlying health conditions, and you don’t want to inadvertently make your dog sicker. Additionally, supplements and herbal remedies can interact unpredictably with any medication or even other supplements that your dog is taking.
Always talk to your vet before you give your dog any new supplements, vitamins, or herbal remedies because they can tell you what might safely benefit your dog, and the correct dosage to use.
If your dog has been diagnosed with IMHA, their prognosis will vary depending on how severe their condition is and how well they respond to treatment.
Dogs who receive prompt treatment and respond well to it have a good outlook. They will usually require medication for a few months, but they can often go on to live normal and happy lives. However, your dog’s prognosis will also depend on whether they are suffering primary or secondary IMHA, as they might need alternative treatment if they’re suffering from another condition that has triggered their anaemia.
A small number of dogs might recover from IMHA, only to suffer from a relapse within a year. In these cases, treatment might need to be repeated and their prognosis will depend on how effective treatment is.
However, it’s a sad fact that a number of cases of IMHA in dogs will be fatal. And dogs who do not receive treatment will almost certainly pass away.
Although modern treatment options have improved the care and outlook for dogs with hemolytic anaemia, there is still a chance that your dog might pass away if their condition is severe, or they don’t respond well to treatment.
Written by: Dr Andrew Miller MRCVS
Andy graduated from Bristol University in 2010 and sees nutrition as a foundation for our pet's wellbeing and takes a common-sense approach. We are what we eat, and it shouldn't be any different for our pets.