Lactose Breath Test in Adults: Are Symptoms Predictive of Lactose Malabsorption?

Background/Objective: Lactose malabsorption (LM) is common, yet not all malabsorbers develop lactose intolerance (LI). We assessed whether symptoms recorded during the hydrogen breath test (HBT) predict LM and whether methane (CH₄) measurement adds diagnostic value. Methods : In this retrospective study, 199 adults underwent HBT (January 2022–February 2025). Pre-test and intra-test symptoms were graded on a 0–10 numerical scale; LI was classified as mild, moderate, or severe. LM was defined by a ≥ 20 ppm rise in H₂; CH₄ positivity by a ≥ 10 ppm rise. Statistical analyses were performed to evaluate the association between symptoms and test results. Results : LM was present in 56.8% of patients. Flatulence during testing predicted LM (p < 0.01) and correlated with peak H₂. Severe LI doubled the likelihood of LM, whereas pre-test symptoms had no predictive value. The addition of CH₄ measurement uncovered a further 3.5% of malabsorbers, that the HBT would have missed. Methane production was observed in 19.1% of patients, and higher baseline CH₄ anticipated a greater post-challenge increase. Conclusions : Flatulence recorded during the hydrogen breath test is a reliable clinical marker of lactose malabsorption in an adult population with unexplained gastrointestinal symptoms. Grading intolerance according to symptom severity effectively identifies lactose malabsorbers. Adding methane measurements further increases diagnostic accuracy. Taken together, these findings support an individualized diagnostic pathway that blends gas profiling with standardized symptom scoring—guiding targeted management while sparing patients from unnecessarily restrictive diets.