Introduction
Small Bowel Colonization (SBC) by colonic microorganisms can be clinically classified according to the microbes' nature in Small Intestinal Bacterial Overgrowth (SIBO)or Intestinal Methanogen Overgrowth (IMO)1 . SIBO and IMO present similar clinical manifestations, but SIBO is H2-producing bacteria-related, while IMO is CH4-producing archaea-related2. The invasive and expensive test of jejunal aspirate with the presence of at least >105 bacterial cfu/ml is often considered the gold standard for diagnosing SIBO3,4, but it is currently replaced by inexpensive, more available and non-invasive lactulose (LBT) and glucose (GBT) breath tests (BT)5. LBT is also used to estimate the oro-cecal transit time (OCTT). Standardization and interpretation of BT are challenging since exact cut-off values are still lacking.
Aims & Methods
This study aimed to investigate LBT and GBT outcomes in adult outpatients (pts) with suspected SBC, to evaluate any differences between LBT and GBT, and to recognize possible standardized time cut-off values. This retrospective cross-sectional study included pts undergoing BT at the Gastroenterology Unit from January 2022 to April 2023. Behavioural and dietetic indications as well as test execution methods were those reported in the current European Guidelines 20214. SBC was diagnosed by an increase of 10 ppm in H2 and/or in CH4 above baseline by 90 min in a single determination in GBT and two following determinations in LBT. On the day-test, pts completed a symptomatic questionnaire based on Rome IV criteria to evaluate clinical indication. Data were expressed as mean (±DS) and median (95%CI), and analyzed using Mann-Whitney and Fisher tests and Pearson correlation.
Results
206 pts (77.2% F, mean age 46.8 ±17 yrs), of which 107 (51.9%) underwent LBT and 99 (48.1%) GBT. In both groups the principal indication was bloating (71% in LBT and 79.9% in GBT) with no demographic and clinical differences between the 2 groups. Overall 22.3% (46/206) had SBC, 29% (31/107) in the LBT and 15% (15/99) in the GBT. No clinical differences were found between SBC and negative (-ve) pts. Analyzing the SBC group, in LBT 90% of pts were positive (+ve) for H2, while in GBT 78% were +ve for CH4 (p<0.0001); no concordance was found between the 2 tests, since among the 26 pts undergoing both BT, only 1 presented positivity in both LBT/GBT, resulting in IMO. The median peak time in LBT [60 min (54-75)], albeit longer, was not statistically different from the GBT peak time [45 min (15-75)]. In LBT-ve pts, median OCTT was 120 min (105-135) for H2 and 150 min (108-191) for CH4 (p=0.12). SBC-OCTT [150 min (135-150)] was statistically longer than -ve-OCTT (p=0.03), suggesting that an increased OCTT represents a risk factor for SBC. Finally, in -ve LBT a weak positive correlation between age and OCTT was found (r=0.36, p=0.003), confirming that age progression may slow intestinal transit.
Conclusion
Peak times within 60 min in LBT and 45 min in GBT can be proposed as diagnostic for SBC. SBC diagnosis do not match between LBT and GBT, which detect distinct gas-producing microbes. LBT result more accurate in diagnosing SIBO, while GBT in diagnosing IMO. Moreover, the SBC detection rate is almost double in LBT compared to GBT, suggesting that GBT may underdiagnose SBC, especially in the distal small gut where H2-producing bacteria seem to be predominant. Therefore, LBT and GBT detect two different SBC conditions, resulting in complementary and non-interchangeable tests that should both be performed when SBC is suspected.
References
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