Ask Dr. Richards: July 2014

Should They Test Their Abyssinians for IMHA?

Q. My husband and I breed Abyssinians, and we were told by another breeder that we should be checking our cats for immune-mediated hemolytic anemia (IMHA), as she owns a relative that tested positive. We don’t know anything about IMHA. Could you enlighten us?

A. Thanks for contacting us about this issue, as anemia (low-red blood cell concentration in the blood) can be a serious problem. Remember that blood is a bodily fluid composed primarily of water, with various types of cells suspended in it. One of these cell types is the red blood cell, which carries oxygen to the tissues of the body.

This oxygen is ultimately used to create molecules that can be used as a source of energy for the myriad biochemical processes that sustain life. Anemia can limit the amount of oxygen that is delivered to the body, thereby limiting the amount of energy that is ultimately available to carry out these vital processes and predisposing to organ dysfunction and symptoms including weakness and lethargy. Depending upon the magnitude of the anemia (i.e., how low the red blood cell concentration gets), anemia can be potentially life threatening and requires immediate evaluation by a veterinarian.

IMHA refers to a situation in which the body’s immune system makes antibodies against its own red blood cells. Antibodies have evolved as a mechanism to protect the body from invading organisms such as viruses, bacteria and parasites; and when they function appropriately, antibodies result in the recognition of these infectious agents as “non-self” and the labeling of them for ultimate destruction by other components of the immune system. When antibodies are inappropriately directed toward red blood cells (i.e., toward “self”) however, they can cause their destruction, leading to anemia and decreased oxygen delivery as outlined above.

IMHA has been roughly divided into primary and secondary classifications. Secondary IMHA refers to situations in which the surface of red blood cells is altered by things like viruses, parasites or toxins, resulting in their inappropriately being labeled as “non-self” and destroyed. Certain types of cancers and infections such as feline leukemia virus and feline infectious peritonitis and drugs such as methimazole and trimethoprim sulfonamides can predispose to secondary IMHA in cats.

Primary IMHA refers to situations in which antibodies are directed against red blood cells, and no evidence of an infectious, toxic or cancerous agent that would cause alteration of the red blood cells is found. Primary IMHA is relatively rare in cats, although recent studies suggest that it is more prevalent than was previously suspected.

The treatment of IMHA is usually directed toward addressing/eliminating potential causes (as may be seen with secondary IMHA), restoring appropriate red blood cell concentration via transfusions if necessary, suppressing the immune response with immunosuppressive drugs such as corticosteroids, and generalized supportive care. Whether therapy for IMHA requires hospitalization or can be provided on an outpatient basis depends upon its cause and severity. The prognosis for cats with IMHA is dependent upon the underlying cause, the severity of the anemia and the stage at which it is diagnosed.

While I am not aware of Abyssinians being predisposed to IMHA per se, they are genetically predisposed to another cause of red blood cell destruction and anemia: pyruvate kinase (PK) deficiency. PK is an enzyme that is crucial for normal energy metabolism in red blood cells, and a deficiency of this enzyme results in their being fragile and predisposed to rupturing, rendering them unable to carry oxygen. Cats can be tested for PK deficiency using a small blood sample, and perhaps this is the test that this breeder is referring to.

I suggest that you discuss these issues with your veterinarian, and consider testing your babies to determine their PK status. This knowledge would be helpful in determining the risk of your kitties for anemia mediated by deficiency of this enzyme and may alter recommendations regarding monitoring for anemia and preparedness for managing anemia should it arise. I hope that this is helpful, and please keep in touch. —Best regards, Elizabeth ❖