13C and H2 breath tests to study extent and site of starch digestion in children with cystic fibrosis

Background: Starch is an important source of energy for children with cystic fibrosis, but little is known about their capacity to digest it. Methods: A C-13 breath test was used to measure starch digestion and oxidation in 16 children with cystic fibrosis (median [range] age, 7.9 [4-15] years; 7 girls, 9 boys) and 5 normal healthy control subjects (median age, 8.3 [7-13] years; 3 girls, 2 boys). A test meal of C-13 flour and lactulose was consumed and breath samples were obtained half-hourly thereafter for 6 hours to measure C-13 enrichment by isotope ratio mass spectrometry and H-2 by electrochemistry. The test was repeated on 10 children with cystic fibrosis when they were taking pancreatic supplements. Results: The median (range) cumulative percentage C-13 dose recovery (cPDR), was 35% (18-52%) in control subjects, 18% (9-33%) in children with cystic fibrosis without enzymes, and 29% (22-51%) in those with pancreatic supplements, cPDR differed significantly between healthy control subjects and children with cystic fibrosis without enzymes (p = 0.01) and between children with cystic fibrosis with and without enzymes (p < 0.0001), but there was no difference between control subjects and children with cystic fibrosis taking enzymes (p = 0.5). Eight children with cystic fibrosis had a cPDR within control range,and in six there was a second peak in (CO2)-C-13 enrichment coincident with an increase in H-2. Conclusions: Starch digestion and oxidation are diminished in children with cystic fibrosis, but pancreatic enzymes restored them to near normal levels. A second peak in (CO2)-C-13 enrichment, suggestive of colonic starch fermentation was absent in healthy children, but present in some children with cystic fibrosis and abolished by pancreatic enzymes.