Established indications for carbohydrate breath tests and symptom assessment include intermittent diarrhea, abdominal pain, bloating, distension, nausea, and flatulence in patients without evidence of organic disease on appropriate investigations and in whom carbohydrate intolerance is considered a possible or likely cause of symptoms.

Results of hydrogen breath testing with symptom assessment for lactose malabsorption and intolerance have acceptable sensitivity and specificity for a clinically relevant condition and can direct effective therapy.

In general, documentation of lactose malabsorption and intolerance indicates the need for dietary treatment. To avoid unnecessary dietary restriction and possible negative outcomes, recommendation of an elimination diet or the use of enzyme supplements (e.g., containing lactase for lactose intolerance or xylose isomerase in the case of fructose intolerance) should be limited to cases in which the relationship between ingestion of the carbohydrate and development of symptoms has been documented.

• Breath testing should be delayed until at least 4 weeks after finishing antibiotic therapy.

• Breath testing should be delayed until at least 2 weeks after colonic cleansing for endoscopic or surgical procedures.

• For a minimum of one day before breath testing, foods containing poorly absorbed, fermentable carbohydrates and dietary fibers should be avoided (e.g. lactose, fructose, xylitol and other fermentable oligosaccharides, disaccharides, monosaccharides and polyols).

• A minimum fasting period of 8 h should be observed before breath testing. 

• To reduce the risk of H2 production from oral bacteria, the oral cavity can be rinsed with an antiseptic solution (e.g., chlorhexidine) immediately before the first (baseline) breath measurements are obtained.

• If the baseline H2 concentration before carbohydrate ingestion is ≥15 ppm, tested persons should rinse their mouth with tap water and then provide a next breath sample. 

• Smoking shall be avoided on the day of the test at least 2 h before and during the duration of the test.

• Physical activity shall be limited for 2 h before and during the test to prevent the influence of respiration on breath H2 values.

• Drugs that contain fermentable carbohydrates (e.g., lactulose or lactose in gram doses), prokinetics, laxatives and probiotics should be stopped at least 24 h prior to breath testing, if possible.

• A diluted solution of a defined dose of carbohydrates in about 300 ml water is appropriate for hydrogen breath testing and symptom assessment.

• The dose of test substance in adults should be 50 g of lactose for the lactose breath test, 25 g for the fructose breath test, 10 g for the lactulose breath test, or 75 g for the glucose breath test.

• The recommended test duration is 3 h, or shorter if a positive diagnosis for malabsorption and intolerance is confirmed.

• The standard measurement interval to assess malabsorption and intolerance is 30 min. 

• A H2 cut‐off ≥ 20 parts per million increase above baseline at a single time point during the test shall indicate maldigestion or malabsorption.

• Several factors affecting the intestinal microbiota, gut motility and the individual sensitivity may result in false positive and false negative results:

• False negative results for carbohydrate malabsorption by breath testing may occur in patients with low H2 excretion (H2 non‐excretion is reported in up to 10% of patients), in those with slow oro‐cecal transit time in whom carbohydrate fermentation commences after conclusion of the breath test and in patients with elevated baseline H2 concentration.

• False positive results for carbohydrate malabsorption by breath testing may occur in small intestinal bacterial overgrowth or in rapid oro‐cecal transit time.