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

Based 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 180minutes. However, using scintigraphic monitoring of lactulose transit time, mean oral-cecal arrival time has been reported as 73minutes. The goal was to propose new criteria for analysing the LBT to overcome false positive interpretations.

LBTs from our referral center were interpreted as positive after ingestion of 10g of lactulose using the following approach for hydrogen concentrations: (1) The literature guidelines: greater than 20ppm from a baseline less than 10ppm achieved within 100minutes followed by a further rise of greater than 15ppm within 180minutes. (2) The proposed criteria: greater than 20ppm from a baseline less than 10ppm within either 60 or 80minutes followed by a further rise of greater than 15ppm during the 180-minute test.

A total of 153 patients with symptoms suspicious for small-bowel bacterial overgrowth underwent testing. Of all, 26.1% patients tested positive by 100minutes, 11.8% patients tested positive by 60minutes and 18.3% patients tested positive by 80minutes. The percentage of positive LBTs at 60 and 80minutes was significantly lesser than for the 100minutes criteria (P < 0.05).

The first hydrogen peak increase should occur by either 60 or 80minutes to increase the specificity of LBT for small intestinal bacterial overgrowth based on the reality of lactulose cecal arrival times.