Immune-Mediated Hemolytic Anemia And Immune-Mediated Thrombocytopenia
Immune-mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP) are
diseases in which the body’s own immune system attacks its red blood cells (IMHA) or platelets (ITP).
Symptoms that develop are caused by massive, often sudden, depletion of red blood cells or platelets.
One of the major functions of red blood cells is carry oxygen from the lungs to all other tissues in the
body. When there are inadequate numbers of red blood cells (anemia), the body becomes starved for
oxygen. As the pet owner, you may notice:
 Depression
 Listlessness
 Panting
 Loss of appetite
 Weakness
 Reluctance to exercise
The major function of platelets is to help form blood clots to stop bleeding. Destruction of large
numbers of platelets may result in pinpoint bleeding in the skin or gums, or may appear as nosebleeds.
Furthermore, blood may be seen in the stool (which takes on a black appearance if it is digested or a
bright red appearance if it is not) or urine. Severe anemia may result from excessive bleeding.
Occasionally, IMHA and ITP occur together (ie: Evan’s Syndrome).
IMHA and ITP are more commonly seen in dogs than cats. You should remember, however, these
conditions may develop in any dog or cat of any age, either sex, neutered or not. There is no scientific
evidence these diseases are caused by anything you feed your pet or by where your pet lives.
Both IMHA and ITP may be classified as “primary” or “secondary.” In primary disease, no underlying
cause of the immune destruction may be found after an exhaustive clinical and laboratory evaluation.
In comparison, secondary IMHA or ITP occurs when the immune system inadvertently destroys its own
red blood cells or platelets secondary to an immune attack directed against an underlying condition
such as cancer, infection, a drug, or toxin exposure. If an underlying condition is present, it is critical to
attempt to correct that problem while simultaneously treating the immune disease.
Treatment of IMHA and ITP relies on suppressing the immune system’s attack against red blood cells
and platelets, respectively. The medications most commonly prescribed to slow down the immune
system are immunosuppressive drugs. Side effects of these drugs may include:
 Increased water intake
 Increased urination
 Increased appetite
 Panting
 Bone marrow suppression
Cats tend not to have significant side effects. Therapy must be continued until there is laboratory
evidence anemia has resolved and there is no ongoing destruction of red blood cells or platelets. This
requires frequent recheck examinations to monitor the success of therapy. If the immune system has
been adequately suppressed, the dosage of prednisone may be slowly tapered continued, often over a
period of several months, and potentially ultimately discontinued. However, please note a majority of
patients living with IMHA and/or ITP typically require some level of immunosuppressive therapy for the
rest of their lives. Please know frequent rechecks are extremely important. If inadequate suppression
of the immune system occurs, alternative drugs are available.
In some dogs and cats, the destruction of red blood cells or platelets is so severe that a life-threatening
anemia may occur. Blood transfusions may be necessary to stabilize these pets until the bone marrow
may keep up with the demand for red blood cells and platelets, and until the drugs suppressing the
immune attack have had time to work.
Prognosis for both diseases is highly variable and depends on the underlying causes if one is present,
and the response to treatment. Relapses may occur months to years after the initial episode. Overall,
if there is no severe underlying illness or significant complications or if your pet responds to therapy,
prognosis for both diseases is generally good.
Please notify us by calling should any of the following occur:
 Your pet seems weak or depressed
 Your pet refuses to eat
 Your pet seems short of breath
 Your pet has blood in the stool or urine
 Your pet has nosebleeds or hemorrhages of the gums, eyes, or skin
 Your pet’s gums and/or tongue seem pale
 Your pet’s signs recur after an apparent recovery