Thymidine Kinase: What One Blood Test Can Detect In Your Cat

If your cat has been experiencing unexplained weight loss and vomiting or diarrhea, your veterinarian may perform abdominal radiographs and routine blood panels. While such tests may reveal certain abnormalities, they do not always provide conclusive diagnostic results. A specific blood test may become a key tool in differentiating between two common diseases that are found in the gastrointestinal tract and achieving a more accurate diagnosis. Find out what this test can detect and what it can mean for your cat's prognosis.

Inflammatory Bowel Disease

Feline inflammatory bowel disease refers to a collective group of chronic diseases of the gastrointestinal tract. Inflammatory bowel disease is characterized by a thickening of the intestinal walls that is caused by the infiltration of inflammatory cells. This compromises the gastrointestinal tract's ability to function normally. Symptoms of inflammatory bowel disease include any of the following:

  • Vomiting
  • Diarrhea
  • Weight loss
  • Changes in appetite
  • Lethargy

Cats with inflammatory bowel disease are typically treated with dietary therapy and medications, and with diligent monitoring, they can live comfortably for years. However, the only way to achieve a definitive diagnosis of inflammatory bowel disease is to perform a biopsy to remove tissues from the full thickness of the intestinal wall for analysis. A much more serious disease that presents with similar symptoms may be the culprit, and it cannot be managed with dietary therapy.


Lymphoma is a malignant type of cancer. It is a cancer of the lymphatic system, which runs throughout the body. In cats, lymphoma accounts for one-third of malignant cancer diagnoses, and it is most commonly found in the cat's gastrointestinal tract. An ultrasound can reveal masses and inflammation, but such inflammation may be caused by inflammatory cells, which cause inflammatory bowel disease, or by cancerous cells, which cause lymphoma. The only way to differentiate the two to achieve a definitive diagnosis is to perform a biopsy, which must be obtained while the cat is anesthetized. Such invasive measures may soon be avoidable, thanks to a specific blood test.

Thymidine Kinase

Thymidine kinase is an enzyme that helps to synthesize DNA that is produced during cellular division. In a healthy cat, the level of thymidine kinase in her blood serum is within a normal range. However, cancer cells divide rapidly, which means that more DNA is being produced, and so more thymidine kinase is needed to keep up with the DNA synthesis. In a cat who has lymphoma, the level of thymidine kinase in her blood serum is significantly higher than the normal range, according to a study described in the U.S. National Library of Medicine National Institutes of Health. These findings have led to the use of a test that helps to diagnose and monitor lymphoma in cats.

TK Feline Cancer Panel

The TK feline cancer panel evaluates the level of thymidine kinase as well as of haptoglobin, a type of protein produced by the liver in response to inflammation. This goal of this test is to differentiate the cellular activity of lymphoma from that of inflammatory bowel disease. The test may be even more helpful for monitoring a cat's response to treatment once a diagnosis is achieved. If the TK feline cancer profile reveals a high level of thymidine kinase and is subsequently treated for lymphoma, a sharp decrease in this enzyme will be indicative that the cancer treatment is working.

Ultimately, the ability to monitor thymidine kinase levels in cats who have undergone cancer treatment and achieved remission can be a boon for veterinarians in their quest to extend the survival time of their feline lymphoma patients.