Immune Mediated Hemolytic Anemia in Dogs

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Key takeaways

Immune-mediated hemolytic anemia (IMHA) in dogs is a condition where the immune system destroys red blood cells. 

  • Primary IMHA (most common) is of unknown cause, while in secondary IMHA, a cause is identified
  • Some examples of causes of secondary IMHA are bloodborne pathogens, cancers of the bloodstream, abnormal drug reactions, incompatible blood transfusions, and presence of another immune-mediated disease such as lupus
  • Symptoms are lethargy, weakness, pale gums, red urine, and nonspecific signs such as vomiting, diarrhea, and lack of appetite
  • Diagnosis is complicated and involves an exhaustive search for an underlying cause
  • Treatment is supportive care and immunosuppressant drugs, usually corticosteroids
  • Prognosis is very guarded; around 50% of dogs with IMHA die during initial hospitalization
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A closer look: Immune Mediated Hemolytic Anemia in Dogs


The red blood cells act to deliver oxygen throughout the body while the immune system acts to protect the body from foreign invaders. In cases of immune disease, the immune system treats normal parts of the body as a foreign entity in need of removal. In the case of immune mediated hemolytic anemia (IMHA), the immune system targets the red blood cells for destruction, reducing oxygen levels in the body and causing serious effects. Signs of IMHA (lethargy, rapid breathing, weakness or collapse, pale gums) are serious and warrant immediate veterinary intervention. Dogs can show mild, slow-developing signs and not appear to be in any pain, or they can suddenly be in severe crisis and require emergency care.

Risk factors


Symptoms of IMHA vary in severity depending on the speed and degree of red blood cell destruction. Dogs with rapid red blood cell destruction have more severe, rapidly developing symptoms compared to dogs where there is slow cell destruction.

Dogs in areas of the world where bloodborne infections are common may be at a higher risk of developing IMHA. Dogs with predisposing factors to conditions associated with secondary IMHA are also at higher risk.

IMHA is uncommon in dogs and carries a guarded prognosis.

Possible causes


The causes of IMHA depend on whether it is primary or secondary. Primary IMHA may be due to:

  • Unknown cause (idiopathic/cause cannot be identified)
  • Possible breed predisposition

Main symptoms


Testing and diagnosis


No single test is definitively diagnostic for IMHA. Instead, evidence from various analyses is used to determine diagnosis. An exhaustive search for underlying causes of IMHA is critical as treatment success is dependent upon removal of triggering conditions, if present.

Next steps include physical examination, bloodwork, including specialized antibody testing, urinalysis, blood smear evaluation and infectious disease testing (diagnostic imaging and bone marrow analysis). Referral to an internal medicine specialist may be made.

Steps to Recovery


If IMHA is suspected, supportive therapy, including fluid therapy, blood transfusions, and oxygen supplementation are performed immediately while diagnostics are ongoing.

Treatment involves targeting the underlying cause, if present, through medication, surgery, or symptom management. Long-term follow up is required to ensure red blood cell levels remain stable.

IMHA is difficult to treat and some dogs do not respond to treatment. Side effects of the medications can be severe. Many patients are euthanized due to poor prognosis.

IMHA is a severe disease and approximately 50% of dogs die during initial hospitalization. Dogs that recover from the initial disease episode are at risk of relapse, often months or years later.

Prognosis is variable even with treatment. Treatment is labor-intensive and side effects from medications can be severe. Further, since RBC counts and overall stability are often erratic in these patients, regular checkup appointments are needed after the condition has stabilized.

Prevention


There is no specific prevention for IMHA, and it is not contagious. Potential risk factors such as viruses and parasitic infections may be contagious, and can be prevented by good routine care and appropriate parasite prevention medications. Always consult a veterinarian before choosing external parasite control. Many available products are toxic to pets, especially cats.

Is Immune Mediated Hemolytic Anemia in Dogs common?


IMHA is rare in dogs.

Typical Treatment


Supportive care:

  • Fluid therapy
  • Blood transfusions
  • Oxygen supplementation
  • Proper nutrition

Therapeutic treatments:

  • Steroids
  • Immunosuppressant drugs
  • Anticoagulants

Other specific treatments:

  • Splenectomy (last choice)
  • Cancer removal and/or treatment
  • Anthelmintics/antiparasitic drugs

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