What are the Causes of Low WBC in Cats?

A low white blood cell count, also called leukopenia, can indicate any number of diseases, conditions or even reactions to medications. Because the causes are so diverse, further testing is necessary to determine the root of the problem. If your cat has a low white blood cell count, your vet may need to test for infectious diseases, or perform an X-ray or ultrasound to identify causes such as cancer. A low white blood cell count often signifies that the body's ability to fight off disease and infection is compromised.

  1. Medications

    • Many commonly used veterinary medications cause decreased white cell counts. Steroids, such as prednisone, are frequently used for a wide variety of feline conditions. These drugs can reduce inflammation and help a sick animal feel more comfortable, but they can also cause a low white blood cell count. According to the Washington State University College of Veterinary Medicine, many chemotherapy drugs also reduce WBC. Cats receiving any medication long-term should receive regular blood work to monitor their WBC and other factors.

    Cancer

    • Several forms of cancer cause low white blood cell counts, and regularly monitoring your cat's WBC may help you spot cancer early. Lymphoma, for example, starts in the white blood cells, and can affect any part of the cat's body, as in the case of feline renal lymphoma, which attacks the kidneys. Another cancer, leukemia, is a cancer of the white blood cells and can cause several other diseases ranging from kidney disease to anemia. According to The Cat Health Guide, leukemia accounts for about 50 percent of all feline cancer cases.

    Chronic Diseases

    • A cat's white blood cell count may decrease as a result of long-term illness. Chronic kidney and liver disease can reduce white blood cells, as can Cushing's Disease and chronic pancreatitis. Cats with bone marrow disease also frequently have lowered white blood cell counts. If your cat has a low WBC, your vet can perform disease-specific diagnostic procedures, such as blood tests, X-rays, ultrasounds or biopsies to identify if any of these conditions are present. In the case of kidney disease, for example, your vet may perform what's called an Early Renal Disease Detection test.

    Infectious Diseases

    • Several viral, infectious and contagious diseases can cause a cat's white blood cell count to plummet. Feline Immunodeficiency Virus, or FIV, is similar to the human disease HIV, and is sometimes called "Feline HIV" or "Feline AIDS." According to PetMD.com, FIV is in the same category of viruses as HIV, and can lie dormant indefinitely before causing symptoms. It usually spreads via bite wounds or scratches. Another infectious disease, Feline Leukemia Virus, FeLV, also causes low white blood cells. FeLV spreads through the body via the white blood cells and is usually transmitted by respiratory secretions or saliva.

    Cautions

    • There are several kinds of white blood cells and not all are affected the same way by medications or diseases. For example, the medication prednisone can increase the number of white blood cells known as neutrophils, but may decrease the number of white blood cells known as lymphocytes. Your veterinarian will need more than a WBC to diagnose a specific illness in your cat. Before you start treatment for any disease, make sure your cat has received a complete diagnostic workup, including blood tests, diagnostic imaging, a thorough physical exam and in the case of suspected cancer, a biopsy.