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Simultaneous non-invasive measurement of liquid gastric emptying and small bowel transit by combined 13C-acetate and H2-lactulose breath test

The 13C-acetate breath test (13C-ABT) allows noninasive measurement of liquid gastric emptying time (LGET), the H2-lactulose breath (H2-LBT) measures orocecal transit time (OCTT). Because of different test principles, both tests can generally be combined. This would not only spare time and resources but may also deliver additional information on the integrated regulation of gastrointestinal motor functions. Our aim was to define an adequate test protocol and to generate normal values for the combined 13C-ABT/H2-LBT. Twenty two healthy volunteers participated (HV, 12 females, age: 26.5  ±  4.7 years, BMI: 22  ±  2.1 kg m−2). Fasting subjects received 200 ml of an aequous solution containing 150 mg 13C-acetate and 10 g lactulose. Breath samples for H2 measurements were collected before ingestion of the test solution and afterwards at 5 min intervals for 180 min, for 13C measurements sampling intervals were prolonged to 15 min after the first hour. LGET was defined as time of maximal 13C-exhalation, OCTT as increase in H2 of ⩾ 20 ppm above basal. Small bowel transit time (SBTT) was calculated as the difference between OCTT and LGET. Mean [95% CI] values for LGET, OCTT and SBTT were 26 [23–30] min, 85 [68–102] min and 60 [44–76] min, respectively. Normal values for LGET and OCTT corresponded with published data. SBTT was not correlated with LGET (R2 = 0.019; p = 0.546). By contrast, there was a very tight and highly significant correlation between SBTT and OCTT (R2 = 0.933; p < 0.001). Multivariate linear regression analyses confirmed that age, sex and BMI had no significant effects on OCTT or SBTT while LGET was weakly correlated with BMI (R2 = 0.240; p = 0.021). In conclusion, the combined 13C-ABT/H2-LBT allows simultaneous measurement of LGET and OCTT as well as calculation of SBTT.