Immune Mediated Hemolytic Anemia in Cats

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Last updated on
4 min read

Key takeaways

Immune mediated hemolytic anemia (IMHA) is a disorder where the body’s immune system targets its own red blood cells for destruction.

  • In cats, IMHA can occur as a primary disorder or secondary to other disorders
  • Primary IMHA has no known cause while the secondary form occurs due to bloodborne infection, blood cancers, adverse reaction to medication, inflammatory conditions, and other immune-mediated diseases
  • Symptoms include pale gums, lethargy, collapse, jaundice, and rapid breathing
  • Diagnostics include physical examination, bloodwork, blood smear analysis, infectious disease testing, and specialized immune-system marker testing (Coomb’s test)
  • Treatment includes treating the primary disorder, steroids, immune-suppression drugs, blood transfusions, fluid therapy, and oxygen supplementation
  • Prognosis for IMHA is poor and some cats do not respond to treatment
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A closer look: Immune Mediated Hemolytic Anemia in Cats

Anemia occurs when there are not enough healthy red blood cells to carry oxygen throughout the body. Immune-mediated hemolytic anemia refers to cases of anemia caused by the body breaking down its own red blood cells.

IMHA is often deadly and requires rapid and intensive intervention. Symptoms may appear slowly or onset may be rapid and some cats with IMHA may not appear to be in pain. Signs of anemia like loss of appetite and decreased activity are always a cause for concern and require rapid veterinary intervention. Severely anemic cats with pale gums, rapid breathing, and weakness need emergency care.

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Risk factors

Primary IMHA is idiopathic, meaning it has no known cause. It is difficult to identify risk factors for idiopathic diseases.

Secondary IMHA occurs in conjunction with other illness. Risk factors for these other conditions may create higher risk of IMHA in affected individuals. Generally speaking, very young, very old, and immunocompromised cats are at higher risk of the conditions associated with IMHA as well as immune-mediated diseases overall.

Possible causes

IMHA can be divided into two categories, primary and secondary.

Primary IMHA is idiopathic and the reasons for development are for the most part, completely unknown.

Secondary IMHA, which is more common in cats, occurs in conjunction with a number of other conditions.

Main symptoms

Early symptoms like decreased appetite and activity are mild and often go undetected. Once enough red blood cells are destroyed to cause anemia, symptoms progress.

Testing and diagnosis

After a physical examination and medical history, a number of tests can be done to confirm IMHA;

  • Blood smear evaluation
  • Bloodwork
  • Coombs’ test (a specialized test to measure immune system markers in the blood)
  • Infectious disease testing

If the condition is secondary IMHA, identification of the underlying condition is needed to effectively target treatment.

Steps to Recovery

Specific treatment of IMHA is directed at stopping the destruction of red blood cells by using steroids and other immune-suppressing medications.

Supportive care includes:

  • Fluid therapy
  • Blood transfusions
  • Oxygen supplementation
  • Blood thinners or anti-clotting medication (clots are a common complication of IMHA)

Prognosis of IMHA is poor and some cats do not respond to treatment. In addition, the drugs used to treat IMHA can be severe and cause concerning side effects. In some cases, euthanasia is considered a more humane response to the disease.


Given that primary IMHA is largely idiopathic, prevention is unclear. Monitoring for changes in overall pet health and staying up to date with regular veterinary health checks can allow for the disease to be caught earlier.

Secondary IMHA can be most effectively prevented by complying with preventive health recommendations for vaccinations and parasite control while also aggressively managing inflammatory conditions and infections. IMHA is not contagious.

Is Immune Mediated Hemolytic Anemia in Cats common?

IMHA is not common in cats but can be slightly more common in areas where blood borne infectious diseases are more prevalent.

Typical Treatment

  • Steroids
  • Immune-suppressing medications
  • Fluid therapy
  • Blood transfusions
  • Oxygen supplementation
  • Antithrombotic medications


Steven L. Marks - Writing for Merck Veterinary Manual
Steven L. Marks, Allison Kendall - Writing for Merck Veterinary Manual
No Author - Writing for dvm360®
Michael J. Day - Writing for Veterinary Partner
Todd Archer,Andrew Mackin - Writing for Today's Veterinary Practice
Todd Archer, Andrew Mackin - Writing for Today's Veterinary Practice

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