Low WBC in Cats

One of the best diagnostic tools vets have is blood work. A small blood sample can answer many questions about the state of your cat's health and will often point the vet toward the correct diagnosis. A complete blood count (CBC) counts every blood cell in a sample by type. Abnormal cell counts can indicate anything from infection to cancer, depending upon other readings. A low white blood cell count means that your cat is suffering from a virus, bone marrow disorder or a very severe infection.

  1. White Blood Cells

    • According to Pet Place, the average a microliter of blood in a healthy cat contains 5,000 to 19,000 white blood cells (WBCs). There are five different kinds of WBC, the most numerous being neutrophils, which move into infected areas to attack bacteria. Lymphocytes are made in the bone marrow and lymphatic tissues, and are responsible for the production of antibodies. Monocytes move into damaged tissue, where they grow into macrophages that "swallow" foreign invaders, and granulocytes are responsible for allergic responses. Granulocytes are classified as eosinophils or basophils according to structure, but basophils are very rare and are considered a significant finding. When blood work reveals a low WBC count, it means they are all busy in damaged tissues, and not circulating in the blood.

    Viruses

    • Cats are prone to viruses, especially if they spend time outdoors and in contact with other cats. Some viruses are very minor. Calicivirus is a respiratory infection that usually amounts to nothing more than a minor annoyance, while the Feline Leukemia Virus can shorten a cat's life span dramatically. Herpes virus is common among cats, and causes eye and respiratory infections, while Feline Immunodeficiency Virus (FIV) is similar to human HIV, and is a terminal disease.

    Bone Marrow Disorders

    • Leukemia is the primary culprit behind bone marrow disorders in cats. There are many types of leukemia, and they differ from Feline Leukemia Virus in that they are not contagious. While Feline Leukemia Virus is a virus in itself, primary leukemias arise as the result of a separate infection, and may respond to immunosuppressive therapy. Myelodysplasia is condition where the bone marrow fails to produce new blood cells, and can be secondary to Feline Leukemia Virus. Myelofibrosis occurs when normal bone marrow components are replaced with fibrous tissue instead of regenerating normally, and can sometimes occur in response to cancer treatments.

    Severe Infections

    • When a bacterial infection overwhelms the entire body, the WBC count will appear low. Sepsis occurs when the bacteria in the blood begin to circulate throughout the body instead of just the infection site, and it can be fatal if not brought under control quickly. Feline Infectious Peritonitis (FIP) is a virus, but symptoms do not generally reveal themselves until the viral phase is over. The resulting infection, inflammation and fluid in the body cavity is what eventually proves fatal unless the disease is treated early. Toxoplasmosis is a parasite that lives in blood cells and is fatal to kittens, but affected adult cats usually recover with treatment.

    Prognosis

    • Viruses cannot be treated with antibiotics, and must run their course. Symptoms can be treated, and supportive care will promote healing, but the overall health of the cat must be good. Bone marrow disorders and severe infections are more serious, but still treatable. A low WBC count is a symptom of a disease, not a disease itself, so the outcome depends upon the root cause as well as the level of care received.