Comparison of inulin and lactulose as reference standards in the breath hydrogen test assessment of carbohydrate malabsorption in patients with chronic pancreatic exocrine insufficiency.

Although often used as a reference standard in the breath hydrogen test (BHT), lactulose fermentation produces more hydrogen, compared to starch, and may therefore not be ideal. This study compares inulin with lactulose as reference standard in the study of carbohydrate malabsorption. Seventeen patients with malabsorption due to chronic pancreatitis and 15 normal controls were studied. Following overnight fasts, BHTs were performed after ingesting 10 g lactulose, 10 g inulin, and 200 g (16 g highly resistant starch) maize meal. Lactulose fermentation produced significantly more hydrogen than inulin in patients with malabsorption (97 +/- 20 vs 45 +/- 22 ppm x hr; P < 0.05) and controls (43 +/- 18 vs 21 +/- 10 ppm x hr; P < 0.05). Patients produced more hydrogen than controls with both standards (lactulose, 97 +/- 20 vs 43 +/- 18 ppm x hr, P < 0.05; inulin 45 +/- 22 vs 21 +/- 10 ppm x hrs; P < 0.05), suggesting adaptation of the colonic flora. Calculated CHO malabsorption was 2.5 +/- 0.8 vs 5.2 +/- 3.8 g with lactulose and 5.2 +/- 3.1 vs 11.2 +/- 9.6 g with inulin as standards in controls and patients, respectively (P < 0.05). Lactulose produces more breath hydrogen than inulin. Calculation of CHO malabsorption using these standards is therefore not comparable.