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Immune-Mediated Hemolytic Anemia Study Guide

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IMMUNE-MEDIATED HEMOLYTIC ANEMIA (IMHA)
VMED 7482 Hemolymphatic System
Laura Nafe, DVM, DACVIM (SAIM)
BACKGROUND
In the normal dog and cat, autoantibodies directed against red blood cell
antigens are identified by the mononuclear phagocyte system in the spleen
and liver, resulting in destruction and removal of senescent (“old”)
erythrocytes.
Average erythrocyte life span is ~120 days in dogs, ~80-90 days in cats
IMHA is a pathologic condition resulting in PREMATURE destruction of
erythrocytes due to an inappropriate immune response.
PATHOPHYSIOLOGY
Type II hypersensitivity reaction
o Anti-RBC antibodies (IgG, IgM)
o Components of the complement system
Results in premature RBC destruction (hemolysis)
o Many patients have a component of BOTH intravascular and
extravascular RBC destruction (hemolysis)
Extravascular more common than intravascular
Extravascular mononuclear phagocyte system (spleen, liver)
Intravascular complement mediated (often assoc with IgM)
Results in systemic inflammation that can result in any or all of the
following:
o Fever
o Severe neutrophilia (can be as high as 70,000-100,000/uL)
Often have many band neutrophils (1000-8000/uL)
Cats with primary IMHA usually have a normal leukocyte count
o Thrombocytopenia 25-70% of cases
Usually mild/moderate
Can be severe with concurrent ITP (“Evan’s syndrome”)
o Risk of thromboembolism
Many reasons for a hypercoagulable state (more on pg 13)
o Systemic inflammatory response syndrome (SIRS)
Disseminated intravascular coagulation (DIC): 14-45% of dogs
Multiple organ dysfunction syndrome (MODS)
Acute kidney injury (AKI)
Liver disease/dysfunction
Non-cardiogenic pulmonary edema (ARDS/ALI)
Common in dogs. Rare in cats.
Can be primary or secondary to other diseases (eg; infection, neoplasia) or
any immune stimulus!

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