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MGI Newsletter
A Fresh Look at Breath Testing at MGI
Vol. No. 4
Thomas R. McGinn, MD, FACP
In This Issue...
Breath Hydrogen
New Physician
Dr. Marc
Scheer
MGI's Newest
Physician
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Gas, bloating and abnormal bowel movements are common symptoms that
motivate patients to see a gastroenterologist. The list of conditions that can
cause these symptoms is extensive. Common disorders that may present
with these symptoms include irritable bowel syndrome, celiac disease,
carbohydrate malabsorption, and small intestinal bacterial overgrowth. A
carefully performed history and physical exam and a few diagnostic tests
can usually lead the clinician and patient to a diagnosis.
Dr. Thomas R.
McGinn
One type of diagnostic study that MGI gastroenterologists are now
performing in their office is hydrogen breath (H2B) testing. H2B tests measure the
concentration of hydrogen and methane in the air we breathe out. The only source of hydrogen
and methane in the exhaled breath is from gut bacteria metabolizing carbohydrates we ingest.
H2B tests are especially helpful in diagnosing two types of disorders that can present as gas
and bloating: carbohydrate malabsorption (ex. lactase deficiency) and bacterial overgrowth of
the small bowel. A review of the pathophysiology of each of these conditions will help illustrate
how hydrogen breath testing works.
Normal human digestion is very efficient in absorbing protein and fat. Carbohydrate absorption
is more variable and may result in unabsorbed carbohydrates reaching the colon where they
undergo fermentation by colonic bacteria. The gas and liquid products of fermentation result in
the symptoms of gas, bloating and diarrhea. Carbohydrates such as lactose, fructose and
sorbitol have been extensively studied in functional bowel disorders, and their malabsorption
may result in symptoms. H2B testing can be performed to assess for malabsorption of each of
these sugars.
Lactose, found in milk, is a disaccharide composed of galactose and glucose. It is digested by
lactase which is found on the lining of the small bowel. Lactose malabsorption is common and
is due to a lack of this enzyme. Because lactose is not absorbed, it passes through to the colon
where through increased liquid and gas production, it causes symptoms of lactose intolerance.
The most common test available today to diagnose lactose malabsorption is the lactose
hydrogen breath test. In this test, a patient ingests 25 gm of lactose and end expiratory breath
is sampled every 60 minutes for 3 hours, and the hydrogen concentration is measured. An
abnormal test will result in a rise in breath hydrogen of 20 parts per million over baseline
(Figure 1).
This abnormal rise occurs because the
malabsorption of lactose leads to more of the
sugar getting to the colon and the bacteria that
normally reside there. The same principle is
utilized in testing for fructose and sorbitol
malabsorption. At Midwest GI, the breath tests
are performed by Theresa Link, RD, a registered
dietitian with expertise in gastrointestinal
nutrition. If carbohydrate malabsorption is
identified, Theresa is able to give patients
detailed dietary recommendations that can
greatly lessen their symptoms.
Figure 1
H2 breath testing can also help diagnose small intestinal bacterial overgrowth (SIBO). SIBO is
a condition caused by an abnormal number of bacteria in the small intestine. Patients with this
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condition may experience diarrhea, bloating, gas. SIBO has been found in a significant number
of patients who previously had been diagnosed with irritable bowel syndrome. Finding
treatable components of irritable bowel syndrome is a therapeutic goal for clinicians and
patients. SIBO, if found, may offer a different treatment option. Small intestinal bacterial
overgrowth is also a cause of malabsorption in the elderly and in patients with small intestinal
conditions that result in stasis, which promotes the overgrowth of bacteria. In these conditions,
weight loss and malnutrition may occur.
The concentration of bacteria in the GI tract increases over its distance. The stomach is almost
sterile, and the number of bacteria in the small bowel is small. Where the small bowel and the
colon meet, a barrier called the ileocecal valve acts to keep bacteria in the colon from migrating
up the small bowel. Normal gut motility also plays a role in keeping the small intestine relatively
bacteria free.
Testing for bacteria in the small intestine is difficult. Culturing fluid from the jejunum and small
intestine is cumbersome and not very accurate. SIBO can be diagnosed indirectly relatively
simply using H2 breath testing. In this test, a patient ingests a 10 gm. lactulose drink.
Lactulose is used because it is not absorbed, and it is metabolized by gut bacteria into H2 or
methane. Exhaled breath is then collected every 30 minutes for 3 hours and analyzed for H2
and methane. Under normal conditions, it takes about 90-120 minutes for the lactulose to make
its way to the colon. Once in the colon, the breath H2 will rise.
In SIBO, the rise in breath H2 is much earlier, classically followed by a second rise as the
ingested lactulose gets to the colon (Figure 2). Up to 30% of the cases of SIBO are due to
bacteria that produce methane; therefore, both gases are measured in the exhaled breath.
Because this is an indirect test and many factors can affect the test results, false positive or
false negative results can occur. The interpretation of the test results has to be incorporated
into the overall clinical assessment.
SIBO is a treatable condition. Ideally, a nonabsorbable antimicrobial agent is used to
eliminate the offending gut bacteria. Often, a
single course of oral antibiotics in the case of
SIBO or a modest dietary change in the case of
carbohydrate malabsorption can improve a
patient's problem with chronic gas, bloating and
abnormal bowel movements.
Figure 2
Introducing Dr. Marc A. Scheer
August 2012, Marc A. Scheer, DO became the newest addition to our team
of GI Specialists. Dr. Scheer completed his Gastroenterology Fellowship at
the University of Nebraska Medical Center. Click here to read more about
Dr. Marc Scheer and all the physicians of MGI.
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