Rise in Hydrogen Production During Lactulose Breath Test Does Not Represent Oro-Cecal Transit Due to Lag in Peak Fermentation

Abstract

Purpose: Small bowel bacteria plays a role in the pathophysiology of irritable bowel syndrome (IBS) recently proven by small bowel culture. However, questions remain about the role of breath testing in IBS. A recent study suggested that hydrogen production reflects oro-cecal transit time rather than bacterial overgrowth based on 5% arrival of lactulose/technetium in the cecum in IBS (Yu et. al., 2011). The study's conclusions are misleading due to 2 unknowns: 1) time to reach peak H2 production and 2) whether 5% of lactulose is sufficient to produce fermentation. We evaluated the first issue by measuring hydrogen production after combining lactulose with fresh stool. Methods: Healthy subjects were recruited based on no complaints of bloating, gas, diarrhea, abdominal pain or constipation. Exclusion criteria were abdominal surgery other than cholecystectomy or appendectomy, use of antibiotics or prokinetic/antikinetic agents within 30 days, or if a single breath test had ≥3ppm of methane. Stool samples were processed within two hours of passage. Every 20g of stool was mixed with 30mL of PBS. Preliminary study showed 2.5g of stool was ideal for hydrogen detection. Thus, 2.5g of stool was placed in five separate flasks with vented stoppers and incubated at 37C while 0g, 0.5g, 2.5g, 5g or 10g of lactulose was added to each. Twenty cc of gas was withdrawn from each flask at intervals up to 90 minutes and analyzed by gas chromatograph for hydrogen and methane. Results: Seven subjects provided stool samples (3 female, 4 male, mean age=31 years). The amount of hydrogen produced was greatest with 0.5g of added lactulose. This happens to represent the expected quantity of lactulose arrival to the colon in Yu et al. Using 0.5g, peak hydrogen production occurred at 60 minutes in all cases with median peak hydrogen level of 210ppm. Although all subjects were breath methane negative, five had increasing methane in their stool. In 4 of the 5, the peak methane production (median=15ppm) occurred at 60 minutes. Thus, even low methane production did not inhibit the production and detection of hydrogen in this experiment. Conclusion: The arrival of 0.5g of lactulose to the colon would produce hydrogen. However, after mixing with colon flora, maximum hydrogen production does not occur until 60 minutes later. Given this large time lag, the time to rise in H2 does not indirectly measure oro-cecal transit. In fact, breath H2 production at a given moment appears to reflect lactulose fermentation by bacteria that started up to 60 minutes earlier (i.e in small intestine).