H2 breath test

In the 1970s, various breath tests were first introduced into clinical practice by, for example, M D Levitt et al. and D A Schoeller et al. and have since been recommended for diagnostic purposes in both adults and children (Hammer 2021).

In the field of gastroenterology, (hydrogen) breath tests are used in medicine to assess the

- the orocoecal transit time (OCTT) (Häußler 2016).

- used in cases of bacterial overgrowth of the small intestine (SIBO [Rezaie 2017]) (Kasper 2015)

- and are used for the diagnosis of

- fructose malabsorption

- lactase deficiency (Herold 2022),

- carbohydrate maldigestion

- methane-induced constipation (Rezaie 2017)

Among others, the following breath tests are differentiated:

- H2 breath test after lactulose administration (lactulose is a disaccharide, consists of galactose and fructose and does not occur in nature)

- H2 breath test after glucose administration

- H2 breath test after fructose administration

- H2 breath test after lactose BT (Rezaie 2017)

- Methane breath test measurement (Hammer 2021).

- H2- breath test with inulin (Stein 2006).

- 1. H2- breath test

The H2 breath test is a non-invasive and cost-effective test method and represents the gold standard for diagnosing lactose intolerance. The sensitivity of the test is 70 - 100 %, the specificity between 69 - 100 % (de Geyter 2021). The test is thus significantly more sensitive than, for example, the determination of blood glucose or galactose in serum (Stein 2006).

Test performance:

The patient appears fasting (fasting period of at least 8 h [Hammer 2021]) and is given 50 g lactose in 400 ml water. Then the H2- content of the final exspirometric breath is measured at the following time intervals: 30, 60, 90 and 120min (Stein 2006). According to European guidelines, a test duration of 3 - maximum 5 h is now recommended (Hammer 2021).

In the presence of lactase deficiency, bacterial decomposition of non-absorbable lactose in the colon results in an increase of H2 in exhaled air (Herold 2022).

Test Interpretation:

If there is an increase in H2- concentration in alveolar air of > 20 parts per million (ppm), this indicates malassimilation of the test sugar or bacterial overgrowth in the small intestine (Stein 2006).

Possible sources of interference:

There are approximately 2.5 - 15% of breath test results that are falsely negative because, for example, H 2 is not produced or the production of CH 4 is increased (de Geyter 2021).

In addition, a role is played by:

- already high fasting H 2 level

- due to smoking before the test (minimum interval should be 2 h [Hammer 2021])

- high fiber meal the night before

- abnormal gastrointestinal anatomy such as: diverticula, constipation

- oral bacteria (can be eliminated by mouth rinsing with 1% chlorhexidine)

- hyperventilation (this can lead to a decrease in the H 2 concentration in the breath; physical activity should therefore be avoided before and during the test)

- Various medications such as laxatives, spasmolytics, antidiarrheal agents (Hammer 2021)

- ileostoma

- antibiotic administration (it is recommended to perform the test at the earliest 4 weeks after cessation of antibiotics [Hammer 2021])

- Purgative measures such as lavage, laxatives, enemas (here, too, it is recommended that the test be performed no earlier than 2 weeks after completion of the respective measure [Hammer 2021]).

- approx. 10% of the population has a non-H2-producer disorder, i.e. in this group of people the colonic flora is metabolically unable to produce hydrogen from lactose (or from other carbohydrates) (Stein 2006).

- 2. methane measurement (CH 4)

At times, H 2 measurement shows a false negative result. Houben et al. (2015) point out that by additionally measuring methane (CH 4), these false negative results can be avoided.

Test evaluation

Here, an increase of > 5 ppm is already considered positive (de Geyter 2021).

The test for methane measurement is primarily used to diagnose methane-induced constipation. At the beginning of the test, however, a bacterial overgrowth of the small intestine (SIBO) due to carbohydrate malabsorption should be excluded in order to avoid false positive results (Rezaie 2017).

Test Interpretation:

A concentration of ≥ 10 ppm is considered methane positive (Rezaie 2017).

- 3. H2- breath test after lactulose administration.

The test is based on the ability of numerous bacterial strains in the colon flora to break down carbohydrates with the release of hydrogen. During the metabolization of carbohydrates in the human organism, however, the hydrogen is converted into water. Lactulose, a non-absorbable carbohydrate, can therefore be used to determine orocecal time (Stein 2006).

Test performance:

After a 12 h fasting period, the patient is given 10 g of lactulose dissolved in 150 ml of water. Then the H2- content of the final exspirometric breath is measured at the following time intervals: 30, 60, 90 and 120min (Stein 2006).

Test evaluation:

An increase in hydrogen reflects the arrival of the test solution in the cecum (Stein 2006).

- 4. H2- breath test with inulin

This is used to measure orocecal transit time. Inulin, a highly polymerized oligosaccharide (Schumpelick 2011), has significantly lower osmotic effects - compared to lactulose (Stein 2006).

- Test procedure

This is performed analogously to the lactulose H2 breath test. 5 mg (or 10 mg) inulin is used. The amount applied has no influence on the test results. The test duration is up to 10 h (Stein 2006).

- Test evaluation

The test is pathological if the H 2 exhalation increases by > 10 ppm (Schumpelick 2011).

The digestion of lactose requires lactase, which is formed in the villi of the small intestinal brush border. If a sufficient amount of lactase is not present, lactose is metabolized into:

- Carbon dioxide (leading to flatulence)

- Methane (CH4)

- proprionic acid

- Butyric acid (leading to osmotic diarrhea)

- Hydrogen (H2)

H 2 and CH 4 accumulate in the intestine. The gases enter the bloodstream through the intestinal wall and are excreted from the lungs via exhaled air (de Geyter 2021). Both H 2 and CH 4 are produced in the human body exclusively by the anaerobic fermentation of both endogenous and exogenously supplied carbohydrates (Hammer 2021).

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