Functional GI disorders are caused by abnormal functioning of the GI tract. These disorders can be classified by GI symptoms related to any combination of following:

• Motility disorder – Abnormal gastrointestinal contractions
• Visceral hypersensitivity – Increased sensitivity to normal intestinal function 
• Altered mucosal and immune function – Changes in immune system responses at the mucosal membranes of the intestines
• Altered gut microbiota – Changes in the microbe population within the intestines which influence host biology in health and disease
• Altered central nervous system (CNS) processing – Integrated communication of the brain and GI tract is altered

These disorders can be caused by abnormalities affecting any part of the digestive system — including the esophagus, gastroduodenal, small intestine, large intestine, gallbladder, biliary tract, and anorectum.

Common symptoms include abdominal pain with no apparent cause, a burning sensation in the chest, chest discomfort or pain, difficulty swallowing, vomiting, chronic cough, and asthma, as well as excessive flatulence, nausea, constipation, diarrhea, or alternating between constipation and diarrhea.

The exact causes of these disorders are often obscure, but can sometimes be related to stress or unhealthy lifestyle choices such as not consuming enough fiber, not eating meals on a regular time schedule, not getting enough exercise, or leading a rushed and hectic lifestyle.

Diagnosing this group of disorders usually requires a team of medical experts from a variety of fields, as well as nursing staff with extensive knowledge of the digestive system, as most patients will only present symptoms, but not present any physical abnormalities upon initial examination. Moreover, symptoms of the disorder often overlap, for example, patients with GERD (gastroesophageal reflux disease) may experience a burning sensation in the chest along with excessive bloating and constipation, making diagnosis more complex.

Medical professionals generally rely on the Rome IV Diagnostic Criteria, which is the internationally recognized criteria set by the Rome Foundation, but may also work together to determine the most suitable procedure for diagnosis based on an individual’s symptoms.

How Your Doctor Diagnoses Upper GI Disorders

• Gastroscopy 
• High Resolution Esophageal Manometry and Impedance 
• Esophageal pH Monitoring 
• Long GI Study / GI Follow Through 
• Gastric and Small Bowel Emptying Time 

How Your Doctor Diagnoses Lower GI Disorders

• High Resolution Anorectal Manometry and Biofeedback Training
• Colonoscopy 
• Colonic Transit Test 
• MRI Defecography 

Preparation is dependent on the type of examination which will be carried out, and doctors will inform patients beforehand as to which examination method is most suitable. Patients are asked to provide doctors with their medical history, allergies, and any medications that they are taking. They will be asked to abstain from consuming any food or liquids before the examination, with the time frame dependent on the specific method. Usually, doctors will ask patients to fast for a period of 4 to 8 hours prior to most examinations. The patients will also be asked to stop taking acid reflux medications during this time, at least 3 to 5 days before the test. However, all of the aforementioned is at the discretion of the doctor.

There is the chance that examinations of the digestive system causes side effects or complications. One example is that patients who have a catheter inserted into their nose may experience nose bleeds, although this is more likely for patients who take aspirin or any blood thinning medications.