Does a glucose-based hydrogen and methane breath test detect bacterial overgrowth in the jejunum?

Direct diagnosis of small intestinal bacterial overgrowth (SIBO) requires the collection and culture of fluid from the jejunal lumen, with a finding of over 10⁵ viable bacteria per mL. More often, SIBO is diagnosed indirectly, using a non-invasive test of the exhaled hydrogen and methane generated by microbial fermentation when ingested glucose reaches the jejunum. Our objective was to determine how well this breath test detects chronic overgrowth of jejunal bacteria that is unrelated to gastrointestinal surgery.

Eighteen patients reporting symptoms consistent with SIBO received a glucose breath test. On a later day, the jejunal lumen was sampled via aspiration during enteroscopy. Jejunal aspirates were cultured on aerobic and anaerobic media. DNA was extracted from the same samples and analyzed by quantitative pan-bacterial PCR amplification of 16S ribosomal rRNA genes, which provided a culture-independent bacterial cell count.

Combined bacterial colony counts ranged from 5.7 x 10³ to 7.9 x 10⁶ CFU/mL. DNA-based yields ranged from 1.5 x 10⁵ to 3.1 x 10⁷ bacterial genomes per mL. Microbial viability ranged from 0.3% to near 100%. We found no significant correlation of glucose breath test results with either the number of bacterial colonies or with the DNA-based bacterial cell counts. Instead, higher signals in the hydrogen-methane breath test were significantly correlated with a lower viability of jejunal bacteria, at a P-value of .014.

The glucose-based hydrogen and methane breath test is not sensitive to the overgrowth of jejunal bacteria. However, a positive breath test may indicate altered jejunal function and microbial dysbiosis.