Interpreting the Lactulose Breath Test for the Diagnosis of Small Intestinal Bacterial Overgrowth

IntroductionBased on literature review, a positive lactulose breath test (LBT) for small intestinal bacterial overgrowth requires an initial peak value of hydrogen within 100 minutes of lactulose ingestion with a second peak before 180 minutes. However, using scintigraphic monitoring of lactulose transit time, mean oral-cecal arrival time has been reported as 73 minutes. The goal was to propose new criteria for analysing the LBT to overcome false positive interpretations.MethodsLBTs from our referral center were interpreted as positive after ingestion of 10 g of lactulose using the following approach for hydrogen concentrations: (1) The literature guidelines: greater than 20 ppm from a baseline less than 10 ppm achieved within 100 minutes followed by a further rise of greater than 15 ppm within 180 minutes. (2) The proposed criteria: greater than 20 ppm from a baseline less than 10 ppm within either 60 or 80 minutes followed by a further rise of greater than 15 ppm during the 180-minute test.ResultsA total of 153 patients with symptoms suspicious for small-bowel bacterial overgrowth underwent testing. Of all, 26.1% patients tested positive by 100 minutes, 11.8% patients tested positive by 60 minutes and 18.3% patients tested positive by 80 minutes. The percentage of positive LBTs at 60 and 80 minutes was significantly lesser than for the 100 minutes criteria (P < 0.05).ConclusionsThe first hydrogen peak increase should occur by either 60 or 80 minutes to increase the specificity of LBT for small intestinal bacterial overgrowth based on the reality of lactulose cecal arrival times.