Structure and Function of the Gastrointestinal Tract in Dogs
Dr. Bari Spielman
Baseline tests such as a complete blood count (CBC), biochemical profile, and urinalysis are essential, as changes in these tests may suggest infection, inflammation, electrolyte and acid-base imbalances, and/or other organ involvement.
What Types of Diagnostic Tests Are Used to Evaluate the Gastrointestinal Tract?
Numerous diagnostic tests are helpful in evaluating the GI tract.
Serologic tests for viruses, fungi, protozoal and tick borne infections may be indicated. Measurement of certain circulating nutrients in the body (Vitamin B, folate, etc.) may be done to assess the absorption capabilities of the intestines. Specialized tests that look for ingestion and exposure to toxins, such as lead and botulism, may be helpful. Certain immune tests are indicated when immune-mediated diseases are suspected.
Other laboratory tests are used to rule out diseases of the liver, pancreas and other abdominal organs as the cause of gastrointestinal symptoms.
A fecal examination is necessary to rule out parasitism, a common cause of diarrhea in cats and dogs. Sophisticated analysis of the feces for its protein and fat content may also be considered. Microscopic examination and culture of feces for certain bacteria may also be done.
Thoracic (chest) radiographs (x-rays) are needed to evaluate the size/shape of the esophagus, assess for the presence of a foreign object or growth, and assess the lungs for the possibility of secondary pneumonia, which may develop with esophageal disease.
Abdominal x-rays are very helpful in assessing the GI tract. They help to identify enlargement, dilation, and twisting of the stomach and intestines, the presence of fluid and gas within the GI, displacement of the GI tract, the presence of a foreign body or foreign material, and may provide clues to the presence of a tumor. Abdominal x-rays also help to rule out other abdominal diseases and other causes of the animal's clinical signs.
Abdominal ultrasonography is also helpful in evaluating the GI tract. It is a noninvasive procedure that provides information about the GI tract and all the other abdominal organs. Your veterinarian may refer your dog to a veterinary internal medicine specialist for an abdominal ultrasound.
Certain x-ray procedures can be performed that are designed to assess the interior of the GI tract. These tests involve the swallowing or administration by tube, of a substance such as barium, that shows up white on x-rays. These x-ray tests are called positive contrast procedures. Examples of positive contrast procedures include an esophagram (barium swallow), an upper GI series, and a barium enema. These tests evaluate the lining of the GI tract and may detect the presence of a stricture (narrowing), dilation, obstruction, foreign body, mass or ulcers.
Positive contrast studies can also be performed under a type of video x-rays, called fluoroscopy. Fluoroscopy provides a way to watch the movement of the barium material as it passes through the pharynx, the esophagus and stomach. It provides information on the muscular coordination of these structures. Fluoroscopy is only available at certain referral practices and institutions, because it requires specialized, expensive equipment. Your veterinarian may refer your dog to a veterinary internal medicine specialist or a veterinary radiologist for performance of these tests.
Advanced imaging tests such as CT scan, radio-isotope scans, and MRI may be helpful in assessing the abdominal gastrointestinal tract and nearby organs.
Endoscopy and biopsy of the upper and/or lower bowel are often performed when GI tract diseases are suspected. Endoscopy involves the passage of a flexible viewing tube into the upper or lower portion of the GI tract. The interior of the esophagus, stomach, duodenum, anal canal, rectum and lower colon can be examined through endoscopy. Biopsies of the lining of these structures can be obtained through the endoscope, and submitted for microscopic evaluation. Sometimes foreign bodies of the esophagus and stomach can be removed via endoscopy. Biopsies can also be taken of masses that are growing into the center or lumen of these structures. General anesthesia is necessary for endoscopy; however, it is considered a relatively low risk procedure compared to abdominal surgery. This procedure may require the expertise of a specialist and specialized equipment.
Surgical exploration of the abdomen is sometimes needed to examine the GI tract, to establish a diagnosis, and to provide effective treatment of certain GI diseases. The entire abdominal GI tract can be examined by surgically opening the abdomen, and biopsies can be taken from both the inside or from the walls of the GI tract, as well as from surrounding structures.
Diseases of the GI tract are sometimes difficult to confirm, and may require a combination of many of the above tests in order to reach a diagnosis.