Reviewed by: HU Medical Review Board | Last reviewed: June 2016. | Last updated: January 2023
One of the tests that may be used to determine if a patient has irritable bowel syndrome (IBS) is a breath test. Commonly, breath tests are used to measure the amount of hydrogen and methane in the breath. These gases are produced by bacteria.1 Breath tests may be used to determine if the patient’s symptoms are caused by lactose intolerance, small intestine bacterial overgrowth, or another infection.
There is no single test that can determine if a patient has IBS. In fact, a diagnosis of IBS is often determined by several tests coming back normal. This can be frustrating for patients initially since when someone is suffering, they want answers and reasons for what they are experiencing. The symptoms of IBS, including diarrhea, constipation, gas, bloating, are also non-specific and can mimic other conditions.2 Physicians use a variety of tests to determine if the patient’s symptoms are caused by IBS or another condition. The breath test is one of those tests.
What Breath Tests Measure
During a breath test, the air exhaled by the patient is captured and measured. The gases present in the breath are then measured.
In the lactose or glucose hydrogen breath test, the patient is asked to avoid eating unfermented carbohydrates, such as whole grain breads and pasta, and fast overnight. A baseline breath sample is collected with the patient exhaling into a balloon-type container. Then, the patient is given a drink with either lactose or glucose, and the breath is again measured at several intervals to measure the hydrogen levels. A high level of hydrogen may indicate lactose intolerance, small intestine bacterial overgrowth, or H pylori infection.3 In cases of IBS, the breath test is normal.
Small Intestine Bacterial Overgrowth
When a patient reports the symptom of bloating, health care professionals consider that it may be caused by SIBO, small intestine bacterial overgrowth.1 While it is normal to have some bacteria present in the intestines, SIBO is a condition in which the bacteria in the intestine multiply in large numbers to excessive amounts. In addition to bloating, SIBO symptoms include chronic diarrhea, weight loss and nutritional deficiencies. SIBO is most often diagnosed through bacterial culture and breath tests. Breath tests are the preferred method for their simplicity, safety and lack of invasiveness.2
SIBO develops when the normal processes that control bacteria growth are interrupted. Most commonly, this occurs due to diminished gastric acid secretion and small intestine dysmotility. Other causes are disturbances in gut immune function and abnormalities of the gastrointestinal tract.2
Several studies that indicate that SIBO is more prevalent in patients with IBS than in the general public, leading to a theory that SIBO may be the primary cause of IBS. However, this causation is currently unsubstantiated and further research is needed.2,4
Studies have shown that patients with IBS are more likely to be lactose intolerant than the general public. Lactose intolerance means the body has difficulty digesting the sugar lactose, which is found in milk and other dairy products.1 Lactose intolerance is a common digestive condition in adults, and it presents with similar symptoms to IBS, including diarrhea, nausea, abdominal bloating, abdominal cramping and gas.
Additional Tests for IBS
When considering an IBS diagnosis, several tests may be performed. In addition to a physical exam where a symptom history is taken, a physician may also perform blood tests, a stool analysis, a lower GI series (x-ray), a colonoscopy or a CT scan.