Variations in colonic H-2 and CO2 production as a cause of inadequate diagnosis of carbohydrate maldigestion in breath tests

Background: Lactose maldigestion is usually diagnosed by means of the H-2 b reath test. When C-13-lactose is used as substrate, a (CO2)-C-13 breath res t can be performed simultaneously. In an earlier publication we described t he relation between both the H2 and (CO2)-C-13 exhalation in breath and the measured intestinal lactase activity after consumption of C-13-lactose. We found a discrepancy between both breath test results in 36% of the cases. To investigate the possible cause of these incongruous breath test results, we studied gas production from carbohydrate in the colon, using C-13-lactu lose as a non-absorbable substrate. Methods: Experiments were performed in 21 subjects, by applying 5 different doses of C-13-lactulose. Repeatability studies were performed in six of these subjects, using 10 g substrate (thr ee tests with I-week intervals). Results: Both the H-2 and the (CO2)-C-13 e xcretion in breath varied strongly interindividually and intraindividually after consumption of C-13-lactulose. In both cases no dose-response relatio n was observed. A significant positive linear relationship was found betwee n Hz and (CO2)-C-13 exhalation (r = 0.45, P < 0.005). Extrapolation of thes e results to C-13-lactose breath tests indicates that the colonic contribut ion of (CO2)-C-13 production to the total (CO2)-C-13 excretion in breath va ries but is on the average large enough to cause false-negative (CO2)-C-13 breath test results. Conclusions: Excretion in breath of (CO2)-C-13 produce d in the colon during a C-13-lactulose breath test correlates with the brea th Hz excretion. This could explain the occurrence of false-negative (CO2)- C-13 lactose breath tests when colonic gas production is high and false-neg ative lactose Ha breath test results when gas production is low. It can als o explain the improved sensitivity of the combined H-2/(CO2)-C-13 lactose b reath rest compared with both breath tests alone.