A veterinarian presented with a dog with symptoms of colitis (straining to defecate and diarrhea combined with fresh blood and mucus) will normally isolate the problem to the colon. Physical examination findings (including abdominal palpation) are usually normal, although some dogs may be underweight and inappetent or painful on palpation of their abdomen, depending upon the cause of their colitis. The results of a urinalysis and routine blood work, including a complete blood count and serum biochemistry profile, are usually unremarkable, unless the dog’s colitis is caused by a systemic disease.
Fecal samples may be examined for the presence of fungi and gastrointestinal parasites by procedures called fecal floatation, direct fecal smear, fungal culture and/or bacterial culture. Abdominal radiographs (X-rays) and ultrasound are available and may reveal masses, fecal impaction, thickened large intestinal tissues, enlarged lymph nodes or other abnormalities. However, the results of these procedures in dogs with colitis are also usually fairly normal. Ultrasound tends to be a poor screening tool for colitis, because the obstructive effects of air in the colon can cloud the ultrasound results.
The procedure of choice for diagnosing the underlying cause of canine colitis is a colonoscopy accompanied by the taking of multiple biopsies from different places of tissues lining the colon. This procedure requires either heavy sedation or general anesthesia. The veterinarian will insert a wand-like instrument with a camera at its tip through the anus and rectum up into the colon. The camera lets the veterinarian visualize the lining of the colon and identify any areas that appear abnormal, such as those that are bumpy, bleeding, inflamed, red or otherwise just not looking healthy. She also can take multiple biopsy samples of those areas with the help of the camera. Those samples will be submitted to a diagnostic pathology laboratory for microscopic assessment through a process called histopathology. Biopsy samples obtained through a colonoscopy are greatly preferred in the veterinary community over biopsies of the colon obtained through abdominal exploratory surgery (laparotomy), which is highly invasive and can expose the animal to a greatly increased risk of intraabdominal infection. When a veterinarian opens the abdomen and then opens the large intestine, there is an increased chance of having the bacterial content of the colon spill into the free abdominal cavity, with the attendant risk of developing peritonitis or other forms of abdominal infection.
Some infectious causes of canine colitis have the potential to infect people, especially if the people have weak or compromised immune systems. People owning, working with or treating dogs with colitis should take appropriate precautions to ensure that their environment is kept as clean and as well-sanitized as possible.