London Cocker Spaniel Society


IMHA -A Life-Threatening Anaemia in Dogs

IMHA illustrating image

Immune-Mediated Haemolytic Anaemia (IMHA) is a rare condition in which a dog's immune system begins
attacking his or her own red blood cells as if they were foreign invaders. The prevalence of IMHA is unknown. Cocker Spaniels appear to be 3 times more at risk than other breeds, and middle aged spayed females are more commonly affected than males.

IMHA is among the most common causes of life-threatening anaemia seen by veterinarians, so familiarity with the condition will allow pet owners to seek prompt veterinary care for their pets when IMHA is suspected.

Anaemia refers to a deficiency of red blood cells. These cells are responsible for transporting oxygen to all tissues of the body. An insufficient number of red blood cells leads to fatigue, shortness of breath, exercise intolerance, fast heart rate and/or pallor.

There are many causes of anaemia, but in IMHA the shortage of red blood cells is due to destruction of the cells by the immune system. For reasons usually unidentified, the cells become marked for destruction and are either removed by the spleen (extravascular hemolysis) or destroyed while in the bloodstream (intravascular hemolysis).
IMHA may be "Primary" with no identified underlying cause or "Secondary" to another medical problem. About 65% to 70% of cases are primary.

Diseases that can cause secondary IMHA include certain types of cancer, infections acquired from tick bites, heartworm infection, and blood parasites.
IMHA can also be caused by unpredictable reactions to certain drugs (antibiotics, aspirin-like drugs, chemotherapy drugs, Booster vaccinations etc.) or even from swallowing a penny!

Signs of IMHA can be very non-specific. At home, you may observe weakness, lack of energy, collapse, or pale or even jaundiced (yellow-coloured) gums in your pet.

Symptoms of IMHA

Loss of appetite, vomiting, diarrhoea or fever are also possible.

In seeking out the reason for these symptoms, your veterinarian may find evidence of anaemia without any obvious cause, such as trauma leading to blood loss.

Your veterinarian will most likely obtain a basic red blood cell count in the hospital, called a PCV (packed cell volume) and will check for agglutination, which is the blood visibly clotting together, indicating the presence of abnormal antibodies in the blood. A normal PCV in a dog is 35% to 45%. Dogs with IMHA can have a PCV as low as 10% to 15%, which can be immediately life-threatening. A test called a CBC will be sent to a reference laboratory to evaluate a variety of parameters, which can determine the extent of the blood cell destruction and confirm a diagnosis of IMHA.

The next step for a dog with IMHA is to attempt to differentiate primary from secondary forms of the disease with a thorough search for an underlying condition that might be responsible for the anaemia. This is likely to include a full biochemical blood profile evaluating organ function, chest X-rays, testing for infections acquired from tick bites, and an abdominal ultrasound. Certain dogs will also receive clotting tests and/or bone marrow evaluation. If all of these tests are normal, your dog most likely has primary IMHA.

IMHA patients may require hospitalisation in an ICU with aggressive medical therapy, often including a blood transfusion, especially if the PVC is below 12%. Most dogs are given red blood cells obtained from a canine blood bank, although blood from a local donor may be used.

If no underlying cause is identified for the IMHA, your veterinarian will treat your dog with one or more immunosuppressive medications. The most common medication is prednisone, a steroid hormone. Prednisone works by decreasing the activity of the immune system, which is inappropriately destroying the body's own red blood cells. Many dogs with primary IMHA also require a second immunosuppressive drug. These medications come with their own side effects, but their use might be unavoidable when a patient has a serious autoimmune disorder.

A common cause of death in dogs with IMHA is thrombosis, or the obstruction of blood flow through a vessel due to a clot. It is estimated that anywhere from 30% to 80% of dogs with IMHA will die due to a thromboembolic event.

Dogs with IMHA are predisposed to abnormal clotting due to the hyper-reactivity of the immune system during acute IMHA. Low-dose aspirin is commonly used to prevent abnormal clotting; other medications that might be used include low molecular weight heparin or a platelet inhibitor such as Plavix (Rivaoxiban).

The prognosis for dogs who survive an acute episode of IMHA is good. Many of these dogs go into remission and are able to stop taking immunosuppressive drugs, but this process often takes up to six months.
About 15% of dogs will relapse and have another episode of IMHA, but most dogs that receive therapy with prednisone, and additional immunosuppressive drug, and aspirin do not relapse.
If you ever become concerned about the health of your dogs, your veterinarian can help you decide if they require immediate medical attention.

In order to monitor the health of our wonderful breed, we would like to know of any health problems with a particular interest in IMHA. The ANIMAL HEALTH TRUST see 4 cases of this disease a month. That does not include other referral centres or vets treating the condition in house throughout the UK.

If your Cocker Spaniel is or has suffered from this condition or is having ongoing treatment we would like to hear from you.

Please fill in a Cocker Spaniel Breed Council Health Questionnaire. You can either email or send the completed questionnaire to Carol West (Breed Co-Ordinator.) Link for questionnaire -


Research Study

Dr. Steven Friedenberg and the Canine Genetics Lab of the University of Minnesota are working to identify GENE Mutations responsible for the development of IMHA. His goal is to use research to understand the disease mechanism and disease triggers, and also to develop a test that can help breeders decrease the incidence of the disease. He is also interested in using the results of his research to help predict disease severity and response to treatment.

Requirements: He is interested in Cocker Spaniels and Clumber Spaniels, however any dog that has been diagnosed with IMHA, either currently or in the past will be accepted.

A willingness to volunteer a blood sample from your dog for genetics research.

Please Contact Dr Friedenberg (or have your Veterinarian Contact him) at

If you are interested in having your dog donate a blood sample Dr. Friedenberg will discuss with you whether your dog is a candidate for study, and obtain the necessary medical records from you or your dog's vet.

If your dog meets the criteria for the study, he will send your vet a prepaid shipping label to send the blood sample from your dog. You can then schedule a brief appointment with your vet for a blood draw.

Consent Form (pdf) | Study Information for Vets (pdf)