Treffer: Diagnostic Reliability of Glucose and Lactulose Breath Tests: Insights From a Test–Retest Study in Healthy Adults.

Background: Small intestinal bacterial overgrowth (SIBO) and intestinal methanogen overgrowth (IMO) are commonly diagnosed using glucose (GBT) and lactulose (LBT) breath tests. Despite their widespread use, concerns remain regarding their reproducibility and reliability, especially in asymptomatic individuals. This study aimed to evaluate the diagnostic variability and test–retest reliability of GBT and LBT in healthy volunteers. Methods: We conducted a prospective observational diagnostic concordance study in 40 healthy adults. Participants underwent both GBT (75 g glucose) and LBT (10 g lactulose) with hydrogen (H2) and methane (CH4) measured at 15‐min intervals. Testing was repeated 2 weeks later. A positive result was defined as an increase of ≥ 20 ppm in H2 or CH4 level of ≥ 10 ppm at any point during the breath testing. Symptoms were recorded during the tests. Agreement and reliability were assessed using kappa statistics and intraclass correlation coefficients (ICC), respectively. Results: At baseline, 15.0% of participants had a positive GBT and 60.0% had a positive LBT, predominantly for H2. In the retest, 10.0% remained GBT‐positive, whereas LBT results were consistent (60.0%). ICC for GBT was 0.56 for H2 and 0.87 for CH4; for LBT, ICCs were 0.88 and 0.85, respectively. Symptoms occurred more frequently with LBT, and the median time to symptom onset (75 min) coincided with physiological orocecal transit. Conclusions: GBT and LBT showed good test–retest reliability in healthy individuals. However, the high rate of positive LBT results and symptom occurrence suggests limited specificity, reinforcing the need for cautious interpretation and further standardization in breath test protocols. [ABSTRACT FROM AUTHOR]