Dogs and cats with mild diarrhea that are not that sick usually only require minimal testing. Generally just a fecal flotation examination to check for the eggs of intestinal parasites passed in the feces is required. Potential parasites include Giardia, hookworms, roundworms, and whipworms. Cats may have the coccidia parasite as well. Also, a parvovirus test may be appropriate for younger dogs.
Animals that are sick or have chronic diarrhea usually require additional tests. To assess possible underlying causes of the diarrhea, the examining veterinarian first needs to determine if the diarrhea is related to the small intestines, large intestines, or both. Bloodwork is usually ordered to determine how well major organs such as the liver and kidneys are functioning. Red and white blood cell and platelet counts will also be taken. The results can help determine the presence of a bacterial or viral infection. They also will show if the animal is anemic or if there is a fungal infection. For cats in particular, other blood tests that may be helpful include an assessment of the thyroid hormone level, and viral screening tests for diseases such as the feline leukemia virus and the feline immunodeficiency virus.
Occasionally more specialized tests are required, including ultrasound, endoscopy, and x-rays of the abdomen. Ultrasound uses sound waves to help visualize the structures of the different organs, including the intestines, liver, stomach, kidneys, and pancreas. Endoscopy is done under general anesthesia and it requires passing a long flexible probe with a camera through the mouth so that the examining veterinarian can see the stomach and intestines. An endoscopic probe can be inserted into the rectum to view the colon as well. Samples of tissues can be taken and examined under a microscope to diagnose certain diseases. X-rays can be taken of the abdomen to check for any obstructions in the bowel. Barium contrast preparations can also be given to the dog or cat to swallow; this substance will reveal on the x-ray any irregularities or abnormalities within the intestines.
The examining veterinarian will be able to determine which tests are necessary to reach a diagnosis. Some cases may be referred to a veterinary internal medicine specialist.
