Immune Mediated Hemolytic Anemia in Cats

Last Updated on June 3, 2021 by Julia Wilson

At a glance

About: Immune-mediated hemolytic anemia is a disease where the body attacks its red blood cells which are responsible for transporting oxygen around the body.

Causes: The condition can be primary or secondary. Primary IMHA has no known cause. Secondary IMHA can be caused by certain toxins such as onions, drugs or metals, cancer, parasites, and neonatal isoerythrolysis.

Symptoms: Lethargy, yellow eyes and mucous membranes (jaundice), weakness, loss of appetite, dark coloured urine, uveitis, collapse.

Treatment: Address the underlying cause as well as supportive care such as oxygen therapy, steroids to suppress the immune system and blood transfusions.


Immune-mediated hemolytic anemia (IMHA), is a disease that occurs when anti-erythrocyte antibodies destroy the cat’s red blood cells (also called erythrocytes) which supply oxygen to the tissues of the body.


IMHA can be classified as primary or secondary. Primary IMHA is caused by an inappropriate immune response and 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’ and initiates a humoral response (antibody production). These antibodies stick to the red blood cells and target them for destruction (hemolysis) by the spleen.

Neonatal isoerythrolysis (NI) occurs in kittens with type A blood whose mother is type B. Colostrum, the mother’s first milk is produced in the first 24-48 hours after birth and contains high numbers of antibodies to protect the kitten from infection. However, if the kitten is type A and the mother type B, antibodies in the blood attach to the kitten’s red blood cells, causing their destruction.


Symptoms vary depending on the severity of the anemia and may appear suddenly or gradually over time.


Your veterinarian will perform a physical examination of your cat and will want to know your cat’s history and 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 that can bind to the surface of red blood cells.
  • Packed cell volume (PCV): Measures the percentage of red blood cells in a blood sample.
  • Complete Blood Count (CBC): A series of tests that evaluates the cellular components of blood (red blood cells, white blood cells, and platelets).
  • Blood Smear: A small drop of blood is spread over a glass slide and examined under a microscope on a slide. The presence of spherocytes and agglutination (red blood cells clumping together) on a blood smear is 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 blood parasites or infection.
  • An X-ray to look for tumours or metal objects.


Prognosis and treatment depend on the underlying cause of the IMHA and the severity. Where possible, find and treat the underlying cause of the IMHA.

  • Corticosteroids to suppress the immune response.
  • 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.