After obtaining a complete history and performing a thorough physical examination, the veterinary team will perform a serious of diagnostic tests to rule out differential diagnoses and make the definitive diagnosis of inflammatory bowel disease. Differential diagnoses with similar symptoms include liver disease, intestinal bacterial overgrowth, lymphoma, gastrointestinal motility disorder, giardiasis, and food allergies.
Diagnostic tests performed include fecal examination, abdominocentesis, diagnostic imaging (radiography and ultrasound), and gastrointestinal endoscopy and biopsy.
Faecal examination involves obtaining a faecal sample for flotation and culture tests. It is an in-clinic test that is performed to rule out other causes of inflammation in the gastrointestinal tract such as intestinal parasites, giardiasis, or bacterial overgrowth.
Abdominocentesis is a surgical puncture of the abdomen using a needle to aspirate fluid. The fluid contents are then assessed for colour, consistency, and contents. Transudate fluid that has a low protein content and low specific gravity is indicative of inflammatory bowel disease. The fluid will be analysed under a microscope to look for the presence of lymphocytes and plasma cells.
Abdominal imaging is performed to eliminate other causes as well as determine the spread of disease. Ultrasonography is by far superior to radiography in order to assess abdominal organs, localise the spread of inflammation, and measure the thickness of the abdominal wall.
Gastrointestinal endoscopy and biopsy are the diagnostic tests of choice to definitively diagnose the cause of inflammatory bowel disease. The dog is sedated while an endoscope is used to examine internal structures for luminal thickness, erosions, and mucosal lesions. A small sample of the gastrointestinal lumen is collected as a biopsy and sent away to a histopathology laboratory for evaluation. In some cases, veterinarians will obtain a surgical biopsy via an abdominal incision and excision of a tissue sample from the intestinal tract. This is a surgical procedure which involves increased anaesthetic risk and can cause a delay in treatment initiation.