Hydrogen exhalation tests are a widespread gastroenterological examination method due to their simplicity and practicality. The examination is based on the fact that carbohydrates that are not absorbed from the gastrointestinal tract are broken down by bacteria in the digestive system, accompanied by the formation of hydrogen, which enters the lungs through the bloodstream and enters the exhaled air.
Hydrogen exhalation tests can be used for a variety of purposes:
• Lactose (milk sugar) intolerance can be tested via a lactose stress test.
• Contaminated small bowel syndrome via a lactulose stress test.
• Fructose malabsorption via a fructose stress test.
The hydrogen breath test procedure
During the hydrogen breath test, end-of-exhalation air must be blown into a device or into special bags, with the hydrogen content of this air being measured by the device. The datum point is obtained from the average of the measurements before drinking the carbohydrate test substance. If this point is high (greater than 16 ppm), the test should be postponed to another time. After drinking the test substance, additional measurements should be taken every 15-30-60 minutes for 2-7 hours. Complaints during the hydrogen exhalation test should also be recorded, as these should be considered when evaluating the test.
Uncertainty of hydrogen breath tests
Some people have methane-forming bacteria (Methanobrevibacter smithii) in their gut flora, in which case methane is formed from the hydrogen released in the gut, hence the hydrogen is bound up. For this reason, the hydrogen content of the exhaled air does not increase even if an increased amount of hydrogen is produced in their gastrointestinal tract. Others have bacteria that produce hydrogen sulfide in their gut flora, which also uses up hydrogen. For those with an intestinal flora that produces methane and hydrogen sulfide, the hydrogen exhalation test may give a false negative result.
Preparing for the hydrogen breath test
On the evening before the test, you should avoid the consumption of fiber-rich and slowly absorbed carbohydrates (cabbage, legumes, potatoes), because they can lead to prolonged hydrogen excretion. Smoking and physical exertion should be avoided two hours before the start of the test and during the test. The use of drugs and antibiotics that affect intestinal motility or reduce gastric acid production, and the use of chewing gum and menthol candies, should be discontinued. Attend the hydrogen exhalation test on an empty stomach, and immediately prior to the test, brush your teeth without toothpaste and rinse your mouth with tap water.
Lactose breath test
Milk sugar (lactose) is broken down in the gut by an enzyme called lactase. This process, which is vital for infants, normally decreases in adulthood, but due to its benefits during evolutionary development, a genetic modification that has allowed milk to be digested in adulthood became widespread. Lactose is a so-called disaccharide consisting of glucose and galactose, which requires the enzyme lactase to break down. Disaccharides can only be absorbed from the small intestine in a split state. In the absence of the enzyme lactase, lactose is not broken down, cannot be absorbed in the small intestine and enters the large intestine where it is broken down by bacteria. During the breakdown, hydrogen is released, which is absorbed into the bloodstream, enters the lungs through the bloodstream, and is detected during the test.
In adult lactose intolerance, abdominal pain, diarrhea, bloating and nausea develop after ingestion of lactose. The exhalation test used to make the diagnosis following a lactose stress test is therefore unpleasant, while the genetic deviation test is more accurate and causes no discomfort.
Lactulose breath test
Functional, chronic diarrheal complaints and bloating are often caused by an acceleration of the transit rate of small intestinal nutrients or the accumulation of abnormal bacterial flora in the small intestine (called dysbacteriosis, or dysbiosis). Lactulose is not normally broken down in the small intestine, and only bacteria in the large intestine are able to break it down and the hydrogen released in the process becomes measurable. An increase in hydrogen concentration indicates that the test substance has reached the large intestine.
Changes and damage to the intestinal flora play a significant role in the development of diarrhea of various origins and in the emergence of complaints. The decrease in the number of beneficial bacteria and the predominance of certain ’bad’ fermenting, gaseous bacteria or other pathogens alters the metabolic processes in the gut (fermentation, putrefaction). This results in increased gas formation and the formation of harmful by-products, which can lead to diarrhea caused by irritation.
Fructose breath test
The commonly termed fructose intolerance covers two diseases. Hereditary fructose intolerance is a very rare serious condition where fructose is absorbed from the gut, but the liver lacks a special enzyme that converts it to glucose, and the accumulating metabolic product is responsible for the symptoms. The diagnosis is made in infancy. With a fructose-free diet, the disease can be treated well.
In the case of fructose malabsorption (indigestion), fructose is not broken down or absorbed in the small intestine for various, temporary or permanent reasons, so it enters the large intestine and is fermented by intestinal bacteria. This produces acids and gases that are responsible for bloating, abdominal pain and diarrhea.
Here, too, treatment is based on eliminating fructose-containing foods from the diet and then identifying and treating the root causes.
Urea breath test (UBT, Helicobacter breath test)
Helicobacter pylori is the most common human gastrointestinal pathogen, present in 50 percent of people worldwide. In Hungary, the Helicobacter pylori infection of adults is between 50 and 60 percent.
The urea exhalation test for Helicobacter pylori is based on the enzyme-producing property of Helicobacter pylori urease. During the test, the subject takes non-radioactive 13C-isotope enriched urea orally. If Helicobacter pylori is present in the stomach, its urease enzyme breaks down urea into ammonia and bicarbonate containing the 13C isotope. The latter is converted to 13C-containing CO2, which appears in the exhaled air, and the amount of 13C isotope can be determined from the exhaled air sample thus obtained. Intake of isotope-enriched urea only increases the 13C content of the exhaled sample in the presence of Helicobacter; if it is high, it indicates a Helicobacter pylori infection in the patient. For children and pregnant women, a 13C isotope urea breath test is recommended.