What is Immune-Mediated Hemolytic Anemia?

Immune-Mediated Hemolytic Anemia (IMHA),  is a disease in which the cat's own immune system can become directed against its own red blood cells.

What are red blood cells?

Red blood cells (also called erythrocytes) supply oxygen to the tissues of the body. They are also responsible for it's red colour.

What causes IMHA?

IMHA can be classified as primary or secondary. Primary IMHA is caused by an inappropriate immune response & no underlying cause can be found autoimmune-mediated hemolytic anemia (AIHA).

Secondary IMHA is brought about by a drug, toxin (onions, metal objects containing zinc), cancer, parasite or infection which adheres to the red blood cell, altering them to the extent that the cat's own body no longer recognises them as 'self' & initiates a humoral response (antibody production). These antibodies stick to the red blood cells & target them for destruction (hemolysis) by the spleen.

Neonatal isoerythrolysis (NI) is another cause of IMHA seen in nursing kittens. This occurs when a kitten is born with type A blood is born to a queen with type B blood. The queens first milk is known as colostrum. Colostrum is produced in the first 48 - 72 hours after birth & provides newborns with essential nutrients & antibodies which protect the kitten from infection. However, in this case the antibodies attach to the kitten's red blood cells, causing their destruction.

What are the symptoms of IMHA in cats?

Symptoms vary depending on the severity of the anemia & may appear suddenly or gradually over time. They may include;

• Depression
• Lethargy
• Pale or jaundiced (yellow tinged) mucous membranes
• Weakness
• Loss of interest in food
• Increased heart & respiration rate
• Dark coloured urine

How is IMHA diagnosed?

Your veterinarian will perform a physical examination of your cat & will want to know your cat's history & any symptoms it may have been displaying.

Additionally, your veterinarian will perform some tests, which may include;

• Coombs test: Also known as antiglobulin test or direct antibody test, this test is to detect the presence of antibodies which can bind to the surface of red blood cells.
• Packed cell volume (PCV): Measures the percentage of a sample of blood which is occupied by red blood cells.
• Complete Blood Count (CBC): A series of tests which evaluates the cellular components of blood (red blood cells, white blood cells & platelets).
• Blood Smear:  A small drop of blood is spread over a glass slide & examined under a microscope on a slide. The presence of spherocytes & agglutination (red blood cells clumping together) on a blood smear are indicative of IMHA.
• Other tests will be necessary to find out if there is an underlying cause of IMHA. This would include blood tests to look for the presence of parasites or infection.
• An X-ray may be performed to determine if the anemia is cause by a metal object containing zinc or cancer.

How is IMHA treated?

Prognosis & treatment depend on the underlying cause of the IMHA & the severity.

Where possible, find & treat the underlying cause of the IMHA.

Corticosteroids to suppress the immune response, most commonly prednisone is prescribed.

Supportive care such as intravenous fluids where necessary.

Blood transfusion: If the red blood cells have dropped to critical levels then a blood transfusion may be necessary.