A thorough history from the cat’s owner, and a complete physical examination that includes gentle palpation of the abdomen and assessment of the cat’s presenting symptoms, will be conducted in suspected cases of colitis. Most veterinarians assessing a cat with diarrhea and signs of abdominal pain will also take blood and urine samples as part of their initial evaluation. Routine blood and urine tests usually are normal in cats with acute colitis, but they may reveal an underlying medical disorder that is contributing to cases of secondary chronic colitis.
Rectal palpation and fecal examinations are among the first diagnostic tests for cats with signs of large bowel diarrhea. These may involve fecal flotation, direct fecal smear, rectal cytology, bacterial culture and/or fungal culture. The results of rectal and fecal tests can disclose the presence of bacteria, fungi, nematodes, protozoal parasites and other infectious organisms. Abdominal imaging, including radiographs (X-rays), barium enemas and abdominal ultrasound, can help identify impactions, masses or other physical abnormalities that might be contributing to the cat’s symptoms, although abdominal ultrasound isn’t a very reliable screening tool for large bowel disease. These imaging techniques can be time consuming, costly and inconclusive. Specialized tests for diabetes, kidney disease, hyperthyroidism, pancreatitis, feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) may also be recommended, because each of these conditions can cause or contribute to colitis or colitis-like symptoms in cats.
Colonoscopy (an endoscopic examination of the colon), with multiple biopsies of the lining of the large intestine taken from several different locations, is the diagnostic technique of choice for any sort of colon disease. Proctoscopy (an endoscopic examination of the rectum) is also available to look at and take biopsy samples of the terminal end of the large intestine. Both of these procedures are performed under heavy sedation or general anesthesia and typically are only done in severe, chronic cases. The biopsy samples are sent to a laboratory for microscopic assessment by a skilled veterinary pathologist, using a process called histopathology.
Acute colitis is sometimes diagnosed after-the-fact, when the cat’s sudden symptoms of large bowel diarrhea go away on their own without medical treatment, or resolve after a change in diet.
Surgical biopsy samples of the lining of the colon are not routinely taken by entering the abdomen directly through the abdominal wall (this is called a “laparotomy”). Open abdominal surgery increases the patient’s risk of bacterial contamination and systemic infection.