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Tests and Diagnosis for Gas and Bloating

author image Russell Havranek, M.D.
Dr. Havranek completed his undergraduate studies and medical school at the University of Nebraska. He then completed his residency in internal medicine and fellowship in gastroenterology at the University of Texas Health Science Center in San Antonio, Texas. He is board certified in gastroenterology and is the current President and CEO of Gastroenterology Clinic of San Antonio.

Finding a cause for gas and bloating can be very challenging. As mentioned previously, there are many causes for gas and bloating, and the most common one — diet — is the most difficult to evaluate. Furthermore, in patients with visceral hypersensitivity, the workup typically all comes back negative. However, there are several common tests that can and should be done if you are suffering from gas and bloating.

Diet Diary

By far the most common cause of gas in our bowels comes from what we put in them. Things we eat, things we drink and even the medications and supplements we take can all contribute to excess gas production. One of the first things I do for patients with gas and bloating is try to evaluate this issue.

First, we review all their medications and supplements and try to cut out all nonessential ones. Many supplements we take that we think are doing us some good actually contain gluten or lactose or other fillers that can get fermented and cause gas. There are medications that can affect motility or movement through our gastrointestinal tract and slow things down. Common offenders are pain pills, some antidepressants and some cardiac medications.

Once we’ve reviewed supplements and medications, we next dive into the diet. The best way to do this is start a food and symptom diary. Every day for at least two weeks keep track of what you eat and how gassy you feel. At times it’s difficult to even remember what you ate and how you felt yesterday, but when you can sit down and look through two weeks of information it’s much easier to find patterns.

Breath Tests

Three of the most common carbohydrates that can cause gas are lactose (dairy products), fructose (some fruits and vegetables) and sucrose (table sugar). To help rule these out as a cause of gas and bloating you can undergo breath testing. The test itself is easy. You are given a small drink that contains lactose, fructose or sucrose. About three hours later you blow into a machine. If your body has problems processing one of the sugars it will make its way down your bowels to where the bacteria live and they will ferment it into gas. That gas is then absorbed into your system and blown out from your lungs and detected by the machine. If any of the breath tests come back positive we focus our diet restrictions in that area.

Another common cause of gas and bloating, small intestinal bacterial overgrowth, is also detected by breath testing. Typically, your small bowel is relatively sterile, but if it has become overgrown with bacteria they will ferment the sugar in the breath test’s solution and be picked up by the machine in a similar fashion.


Typically, for gas and bloating that doesn’t improve with diet modifications, we start looking deeper. Upper endoscopy is a procedure in which you are given some medication through an IV to make you sleepy and comfortable, and then a small camera is passed through your mouth down into your stomach and small intestine. With this study your doctor can rule out things like celiac disease, parasites of the small bowel, ulcers, gastritis, Helicobacter pylori (bacteria that can live in the stomach) and obstructions or cancers of the stomach.

Radiology Studies

Sometimes gas and bloating occur because fluids and gas can’t move through the gastrointestinal tract like they should. This can be caused either by slow motility or an obstruction (like a tumor). The ways these issues are ruled out are with radiology studies. The most common are:

1) small bowel series (you drink some contrast and X-rays are taken of your bowels)

2) gastric emptying scan (you are given food to eat and your stomach is scanned to see how slow it empties)

3) ultrasound (a probe is placed over your abdomen to look for things like gallstones)

4) HIDA scan (special study that tests the function of your gallbladder)

5) CT scan (a computer-generated scan that looks at your whole abdomen)

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