Breath Hydrogen Test

Diagnostic Use

Please note that due to staffing restrictions, requests will be vetted. Only glucose hydrogen breath tests requested by gastroenterology will be approved at this time.

Primarily used as a non-invasive way to identify carbohydrate malabsorption or small intestinal bacterial overgrowth (SIBO). Normally a carbohydrate load is rapidly digested to it’s smallest constituents (monosaccharides) and fully absorbed. If this cannot happen, due to delayed digestion or gut bacterial activity, microbes will ferment these carbohydrates and produce hydrogen and/or methane.

Testing process

After an overnight fast, hydrogen +/- methane are simultaneously measured from expired breaths at baseline. Then a fixed oral dose of selected carbohydrate is given, followed by measurement of the 2 gases every 30mins for a total of 2 to 3 hours. The baseline gases concentration and the magnitude of rise in relation to time to peak/plateau will be interpreted in light of the type and dose of carbohydrate used and the pre-test diagnostic question.

Interpretation

Depending on the trade-off between sensitivity and specificity for different pre-test probabilities/indications, the criteria for positivity in breath hydrogen/methane test varies widely. Cut points can also differ with the type and dose of substrates used.

Test generally considered as positive (provided timing of the peak occurred as expected) if:

• Hydrogen:
  • More than 20ppm above baseline; or,
  • 2 or more consecutive readings more than 10ppm above baseline

• Methane:
  • More than 20ppm above baseline; or
  • Methane level more than 2 times above baseline

Less stringent criteria than the above can be considered in selected cases to improve sensitivity.

In high methane producers, combined consideration of both hydrogen and methane response may improve diagnostic sensitivity.

Carbohydrate malabsorption

Normally with sufficient disaccharidase activity along small bowel mucosal lining and with adequate small bowel absorptive area, ingested disaccharides like lactose or sucrose are completely hydrolysed and absorbed as monosaccharides like fructose, glucose or galactose.  No rise in hydrogen or methane is expected. However, if the small bowel enzyme activity and/or absorptive area become inadequate (e.g. from lactase deficiency or from generalised gut diseases like e.g. coeliac or Crohn), the unabsorbed lactose will go down to the colon where it undergoes bacterial fermentation with gases released.  Part of the hydrogen from hydrogen producers and/or methane from ‘non-hydrogen producers’ will be absorbed and expired through lungs, causing an observed rise in hydrogen/methane concentration after about 90-120mins – the usual oro-caecal transit time.

While carbohydrate malabsorption can be diagnosed from the above breath test, its correlation with carbohydrate intolerance symptoms like nausea, bloating, abdominal pain and diarrhoea is not straightforward. The correlation between these 2 entities (carbohydrate malabsorption and carbohydrate intolerance) depends on factors like : nature and dose of carbohydrate used in the test in relation to the individual intake practice in real life environment;  co-intake of carbohydrate absorption enhancers or inhibitors; proneness of individual bowel towards heightened sympathetic response from volume distension; presence of sulphate reducing bacteria with H ₂ S production causing direct toxic effect on gut; unabsorbed luminal carbohydrate’s osmotic effect or altered signalling mechanism causing diarrhoea etc. Constipation is more common in high methane producers.

Small bowel bacterial overgrowth

Glucose as a monosaccharide normally is completely absorbed in the proximal small bowel. Thus, it is usually unavailable to colonic bacteria for fermentation to release hydrogen. However, if there is a significant small bowel bacterial overgrowth or rapid bowel transit, the ingested glucose can be fermented in the small bowel to release gases, registered as a peak during monitoring.

In contrast, lactulose as a synthetic disaccharide is normally not metabolised nor absorbed in the small bowel. Thus a late appearance of a colonic peak from colonic bacteria with hydrogen release is to be  expected. However, in small bowel bacterial overgrowth, lactulose will be prematurely exposed to the small bowel bacteria, thus an early abnormal small intestinal hydrogen peak can be observed usually before 90 minutes (assuming normal bowel transit time).

We believe Glucose overall is a better substrate than Lactulose for small bowel bacterial overgrowth (at least for proximal small bowel).  As of 3/9/2012, for all lactulose requests, glucose will be used instead. Lactulose will only be used after prior discussion with and approval by Chemical Pathologist on duty.

High fasting baseline hydrogen / methane values:

This finding can be a result of consumption of poorly absorbable complex carbohydrates like potato, in the evening before the test.  It can also be caused by small bowel bacterial overgrowth, or untreated celiac disease where there is enhanced exudation and prolonged fermentation of endogenous glycoprotein / exogenous carbohydrates.  On the contrary, high fasting methane in methane producers normally is derived from endogenous rather than dietary substrates.