Variations in Colonic H₂and CO₂Production As a Cause of Inadequate Diagnosis of Carbohydrate Maldigestion in Breath Tests

Background: Lactose maldigestion is usually diagnosed by means of the H-2 breath test. When C-13-lactose is used as substrate, a (CO2)-C-13 breath rest can be performed simultaneously. In an earlier publication we described the 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-lactulose 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 (three tests with I-week intervals). Results: Both the H-2 and the (CO2)-C-13 excretion in breath varied strongly interindividually and intraindividually after consumption of C-13-lactulose. In both cases no dose-response relation was observed. A significant positive linear relationship was found between Hz and (CO2)-C-13 exhalation (r = 0.45, P < 0.005). Extrapolation of these results to C-13-lactose breath tests indicates that the colonic contribution of (CO2)-C-13 production to the total (CO2)-C-13 excretion in breath varies 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 produced in the colon during a C-13-lactulose breath test correlates with the breath Hz excretion. This could explain the occurrence of false-negative (CO2)-C-13 lactose breath tests when colonic gas production is high and false-negative lactose Ha breath test results when gas production is low. It can also explain the improved sensitivity of the combined H-2/(CO2)-C-13 lactose breath rest compared with both breath tests alone.