The inulin hydrogen breath test accurately reflects orocaecal transit time

The lactose[(13)C]ureide breath test ((13)C-LUBT) has been validated and established as a reliable, non-invasive test for the assessment of orocaecal transit time (OCTT). More recently, small studies have demonstrated that inulin could be an alternative substrate for H(2)-based breath testing of the small bowel transit (H(2)-INBT). We compared the performance of the H(2)-INBT with the (13)C-LUBT in an appropriate number of participants, determined by sample-size calculation.

Twenty-nine people underwent a combined (13)C-LUBT/H(2)-INBT. Five Hundred mg of lactoseureide was ingested on the day before the test to induce an adequate enzyme activity in colonic bacteria. For the test, they received 500 mg of lactose[(13)C]ureide and 5 g inulin, dissolved in 400 mL of a standard enteral liquid nutrition orally. Breath samples were collected every 30 min for 8 h and analysed for H(2)[ p.p.m.] and (13)CO(2)-enrichment [delta-(13)C]. For the (13)C-LUBT, the OCTT was defined as the interval with an increase of delta > 2.5SD above the running average of all previous points. The latter was defined as a rise of > 10ppm above baseline regarding the H(2)-INBT.

Breath tests produced evaluable data in 27/29 patients [93%]. Median OCTTs were 315 min (range 210-450 min) for the (13)C-LUBT and 300 min (180-420 min) for the H(2)-INBT (P = 0.15). The (13)C-LU-OCTT correlated well with the H(2)-IN-OCTT (r = 0.72). Bland-Altman blot showed that the mean H(2)-IN-OCTTs were approximately 30 min shorter than predicted with the (13)C-LUBT.

Inulin is a reliable and inexpensive substrate for a hydrogen-based assessment of the OCTT. In contrast to the (13)C-LUBT, the H(2)-INBT does not require patients to refrain from physical activity and may additionally increase its acceptance for clinical purposes.