Diagnosis of colitis:
1. History - It is very important to observe and describe accurately all  factors such as the type and frequency of stool, the dog's environment, diet, stress factors, straining, etc.
2. Laboratory analysis - fecal exams are invaluable as a basic part of the patient analysis to determine the presence of parasites, undigested nutrients, and blood. A blood test for evidence of Pancreatic digestive enzyme insufficiency called an TLI Test (trypsin-like immunoreactivity) can be used to evaluate the ability of the pancreas to properly digest food presented to the digestive tract.  There are state-of-the-art blood tests that only a few laboratories can run that will indicate probabilities of specific food ingredients to which the patient may be hyper-responsive.
3. Radiography - Barium, a substance that shows up on an x-ray very well, can be given orally or via enema.  X-rays are very helpful in gathering data about the colon.
4. Colonoscopy - Direct visual exam by a specialist can be very revealing.
5. Biopsy - Often in chronic colitis the biopsy provides the final step in determining a diagnosis as to the cause.  This requires an anesthetic and surgical procedure, therefore, other modes of diagnosis and treatment are employed first. The biopsied specimens are sent to a veterinary pathology lab for what is called a histological exam by a specialist in veterinary pathology. 

Treatment:  
The treatment depends of course upon the cause.  Whipworms in dogs must be ruled out  even if fecal samples are negative; so too with Giardia.  These single celled organism can be very debilitating to dogs and cats.  Antibiotics, proper worming, and adding bran to the diet are employed with varying success.  Food allergy is a multifaceted and difficult-to-manage disorder. There are  special ingredient foods (Therapeutic Diets) now available to help dogs and cats avoid the specific dietary ingredient that triggers the allergic response.  

As a general rule, the treatment of colitis is prescribed and applied according to what the final diagnosis is.  A thorough workup of each case is important because if a treatment protocol is undertaken and the actual cause is something other than the assumed cause, more harm than good can come of the "treatment".  Often a specific  antibiotic will be prescribed that affects mostly intestinal bacteria and is not absorbed systemically like most antibiotics are when used to treat infections outside the intestinal tract.   Cortisone may be the drug of choice for chronic Inflammatory Bowel Disease but would be inappropriate for use in a Giardia infested dog or cat so the diagnosis must be accurate if success is to be achieved. 

Special diets, called Therapeutic Diets, may be prescribed by the veterinarian that contain select ingredients unlikely to irritate the bowel.  In many cases, chronic colitis will require lifelong therapy in order to achieve a good quality of life for the dog or cat.

A Note About Constipation:
One of the most frequently occurring digestive tract disorders of cats is constipation.  Dogs suffer from constipation on occasion, generally from ingesting an unusually large meal of bones or fibrous, indigestible material.  Cats, especially older cats, commonly will be afflicted with constipation. Repeated episodes can lead to a serious condition called megacolon.  The most common reason for intermittent vomiting in a cat (other than to expel hairballs) is constipation.  Click on the x-ray image on the left to see a typical x-ray of a constipated cat.  When the colon is filled to capacity and the ability or impulse to defecate is missing, the colon contents dehydrate and become firmer and dryer.  The longer the stool remains in a static and non-motile large intestine the more difficult it is for the cat or dog to pass that material.  As a result of the constipation the animal looses its appetite and in severe situations might become dehydrated and noticeably sick.  Veterinary intervention maybe required.  Physical examination, and the added informative value of radiography, will assist in determining if constipation is affecting a patient. 

Repeated episodes of constipation where the wall of the colon is stretched and inflamed, may eventually lead to a condition called an Atonic Colon.  In this very dangerous situation the colon wall loses its ability to contract and to propel the stool retrograde along the digestive tract.  The wall of the colon eventually becomes very thin instead of elastic and muscular. Some of these affected cats may need to have the colon removed surgically in order to lead a reasonably healthy and happy life, free from repeated enemas, diets full of fiber, and the ill health associated with constipation.

The TREATMENT for constipation really is determined by the cause.  For intermittent constipation due to sudden ingestion of fibrous, bony, indigestible material, the treatment may be gentle enemas and stool softeners taken by mouth.  For more chronic constipation due to bowel abnormalities (such as poor nerve transmission, stretched bowel wall, megacolon or cancer) each case must be evaluated on an individual basis.