Merck Manual

Please confirm that you are a health care professional

honeypot link
Pet Owner Version

White Blood Cell Disorders of Cats


R. Darren Wood

, DVM, DVSc, DACVP, Department of Pathobiology, Ontario Veterinary College, University of Guelph

Reviewed/Revised May 2018 | Modified Oct 2022

Leukocytes, or white blood cells, in the blood of mammals include neutrophils, lymphocytes, monocytes, eosinophils, and basophils. These cells vary with regard to where they are produced, how long they circulate in the bloodstream, and the factors that stimulate them into going in or out of the intricate network of tiny blood vessels that branch out through the tissues of the body. The normal numbers of each type of white blood cell also vary among species. Leukocytosis is an increase in the total number of circulating white blood cells; leukopenia is a decrease.

Leukograms are blood tests that count the number of different white blood cells circulating in the bloodstream. By counting the cells and examining their form your veterinarian gains valuable information that can help diagnose a wide variety of disorders.

Disorders Related to Increased or Decreased White Blood Cells

Neutrophilia is an increase in the number of neutrophils in the bloodstream and is caused by inflammation. Structural changes in neutrophils may occur during severe inflammation and are referred to as toxic changes. Neutropenia is a decrease in the number of neutrophils in the bloodstream. It may occur due to the white blood cells sticking to the walls of damaged blood vessels, consumption of neutrophils (as a result of severe inflammation), destruction of neutrophils, or reduced formation in the bone marrow. Neutropenia may occur in all species during overwhelming bacterial infections. Adverse reactions to drugs may result in neutropenia or even pancytopenia (a reduction in red and white blood cells and platelets) in cats. Feline leukemia virus and panleukopenia (feline distemper) have also been associated with neutropenia.

Eosinophilia is an increase in the number of eosinophils, which are involved in allergic reactions and in controlling parasites. Increases are caused by substances that promote allergic reactions (for example, histamine) and by certain antibodies. Eosinophils increase during infections with parasites such as fleas. Eosinophilia also may occur with inflammation of the intestines, kidneys, lungs, or skin. Hypereosinophilic syndrome—with persistent and excessive levels of eosinophils, which accumulate in various organs—has been reported in cats. The cause is unknown. Diagnosis may require several blood tests. Less commonly, eosinophilia may be associated with cancer. In some cats, eosinophils collect in skin or mouth sores. A decrease in eosinophils is known as eosinopenia and may occur due to stress or treatment with corticosteroids.

Leukemia and Lymphoma

Leukemia is a malignant cancer that is characterized by an increase in abnormal white blood cells in the bloodstream. Veterinarians may consider leukemia as a potential cause of disease when there is an increase in the number of white blood cells in your cat's bloodstream.

The severity of leukemia varies. Acute (short-term) leukemia often causes generalized signs of illness and has a poor outlook. These animals have abnormal, immature white blood cells in the blood, as well as decreased numbers of other normal types of blood cells (red blood cells or platelets). In contrast, a chronic (long-lasting) leukemia often causes few if any signs and may be discovered by chance, have a longer course, and be more responsive to treatment. These animals usually do not have deficiencies of other types of blood cells. Your veterinarian may be able to estimate your pet's outlook based on the findings of laboratory tests and recommend an appropriate treatment.

Lymphoma is a related cancer of lymphocytes (a type of white blood cell) that often begins in a lymph node or other lymphoid tissue (such as the spleen). However, lymphocytes are present in all organs, and lymphoma can develop anywhere, including the chest, digestive tract, kidneys, central nervous system, eyes, skin, and nose. If laboratory tests show the presence of immature white blood cells in the blood, your veterinarian will likely want to look for cancer in other parts of the body.

Chédiak-Higashi Syndrome

This inherited syndrome occurs in Persian cats (and in humans). There is an increased susceptibility to bacterial infections due to impaired white blood cell function, an increased tendency to bleed due to platelet defects, and partial lack of color in the eyes and skin due to abnormal melanin (pigment) distribution. Diagnosis is based on abnormal skin color, presence of abnormal white blood cells, and increased susceptibility to infections.

Pelger-Huët Anomaly

This inherited condition is characterized by the failure of certain white blood cells (granulocytes) to mature normally. White blood cell function is normal, and many cats do not have any signs of illness. In some animals, it is deadly and associated with skeletal deformities and increased susceptibility to infection.

For More Information

quiz link

Test your knowledge

Take a Quiz!