Introduction
Glucose (GBT) and lactulose (LBT) breath tests have been recommended by international consensus for the indirect diagnosis of small intestinal bacterial overgrowth (SIBO) and the newly introduced intestinal methanogen overgrowth (IMO), based on the variations of respectively hydrogen and methane concentrations in breath avec ingestion of the above-mentioned sugars. UEG consensus has recommended preferring glucose, due to the difficulty to differentiate, with lactulose as substrate, between rapid intestinal transit and true SIBO (1,2).
Aims & Methods
The aims of this retrospective study were to compare the positivity of GBT and LBT in a population of well-characterized patients with IBS. Among 995 glucose (75 grs) or lactulose (10 grs) breath tests performed in our unit between January 2021 and January 2023, wev extracted a cohort of 287 patients with typical IBS according to Rome IV criteria, after exclusion of patients with a past history of digestive surgery (except appendectomy and cholecystectomy), diabetes, neurological diseases, active or in remission IBD, scleroderma and other connective tissue disorders, chronic intestinal pseudo-obstruction, cirrhosis.
Breath tests were performed after a 8 hour fast, and a strict no fiber and fermentable food the day before. GBT or LBT were performed according to the physician request. During the test, patients filled in a standardized questionnaire to evaluate digestive symptoms, anxiety and depression, and food intake disorders. Various cutoffs for the positivy of the tests were used, according to recommendations: + 12 ppm or +20 ppm for hydrogen variations over baseline (SIBO), and values greater than 10ppm for methane (IMO). For LBT, values were considered only between baseline and 90 minutes after sugar ingestion, to limit false positive results in relation with colonic fermentation of lactulose (120 minutes for GBT) (3).
Results
155 GBT and 132 LBT were performed in IBS patients (71% women, mean age 45, mean BMI: 22.6 kg/m2 ). There was no difference between both groups in terms of demographics, IBS type, severity of symptoms, anxiety and depression. Results were clearly different for the positivity of tests: LBT was 10 times more frequently positive than GBT with the +20 ppm cut-off for hydrogen. There was no difference for the positivity of both tests for methane (table 1).
Table 1.
| Glucose (N=155) | Lactulose (N=132) | p value |
| Hydrogen +12 ppm | 12 (8%) | 72 (55%) | 0.0001 |
| Hydrogen +20 ppm | 7 (4.5%) | 62 (47%) | 0.0001 |
| Methane ≥10 ppm | 52 (34%) | 45 (34%) | 1.000 |
There was no significant association between symptoms and the positivity and negativity of the tests, whatever the substrate or the cut-offs. Methane levels were lower in IBS-D patients, and in patients complaining of diarrhea as the predominant symptom (p<0.04).
Conclusion
GBT and LBT are not comparable for the diagnosis of SIBO, in a population of well-characterized IBS patients, without comorbidities The very high prevalence of positive LBT (around 50% of IBS patients would be considered SIBO positive) does not make this test acceptable for this diagnosis. Furthermore, the positivity of both tests for SIBO were not correlated with symptoms, which may indicate a poor clinical significance of this diagnosis in IBS. With regards to IMO, both tests give similar results, mainly because baseline values are taken into account: the prevalence of IMO according to these tests is also rather high, and inversely correlated with diarrhea. The significance of the association between IMO and IBS should be tested in prospective interventional studies.
References
1. Pimentel et al. ACG clinical guideline: small intestinal bacterial overgrowth. Am J Gastro 2020; 115-165-78
2. Hammer et al. European guidelines on indications, performance, and clinical impact of hydrogen and methane breath tests in adults and paediatric patients.
UEG Journal 2021.1-26
3. Shaker et al. Pattern of methane levels with lactulose breath testing; can we shorten the test duration? JGH Open 2021; 5: 809-812.
Disclosure
Nothing to disclose