Many cats with leukemia develop tumors because their white blood cells (WBCs) congregate and create masses in the intestines, the chest, spleen, or kidneys. This form of leukemia is called lymphoma for "lymph" meaning white blood cells, and "oma" meaning tumor. Symptoms depend upon where tumors are located and how they affect normal function. In some cats, the blood will be full of immature white blood cells called lymphoblasts. When the lymphoblasts develop suddenly, the condition is called acute lymphoblastic leukemia (ALL). When lymphoblasts develop slowly, the condition is called chronic lymphocytic leukemia (CLL). Cats with ALL usually die very quickly but those with CLL may go into remission when treated with Chlorambucil or Prednisone.
How are Cats Diagnosed with Leukemia?
Diagnosing feline leukemia is more difficult than one would think given that there are many tests to help with the diagnosis:
- Tear tests
- Saliva tests
- Blood tests
- Bone marrow tests
Diagnosing is difficult because occasionally tests are difficult to interpret or the results are different when cats are retested in a few months.
The saliva test is simple to do, but is less accurate than blood tests. Tests of blood, saliva, or tears can look for specific leukemia proteins. Finding the leukemia proteins does not mean your cat will become ill with leukemia. Some of these cats clear the virus from their bodies completely and never become ill. Because cats can clear an infection, any cat with a positive test is retested in three months to determine whether he or she is infected or has cleared the virus.
It is also possible to diagnose feline leukemia with a blood test that measures the total number of white blood cells. The number of white blood cells (WBCs) in a healthy cat ranges from 5,500-20,000 WBC per mm3 blood. If your cat has leukemia, the number of WBCs can increase or can plummet. While these results suggest feline leukemia, there are other conditions that cause WBCs to increase (infection) or plummet (kidney disease).
There are special, rather complicated bone marrow tests that help diagnose the feline leukemia virus (FeLV), but these are not routinely done. Occasionally, X-rays help diagnose FeLV because they show tumors that rarely develop except with leukemia, such as tumors in the thymus gland in the chest.
Diagnosis of feline leukemia is further complicated because many cats with leukemia are simultaneously infected with multiple diseases. For example, many cats with leukemia also have feline immunodeficiency virus (FIV). When multiple diseases affect blood and bone marrow, it is more difficult to determine what is causing your cat's illness. Often the diagnosis of feline leukemia requires waiting and retesting, which is emotionally draining for the family.