Metabolic handling of 13C labelled tripalmitin in healthy controls and patients with cystic fibrosis.

AIM To examine the gastrointestinal handling and metabolic disposal of emulsified [1-13C]palmitic acid esterified into a triglyceride in nine healthy children and seven patients with cystic fibrosis on enzyme replacement treatment. METHODS After an overnight fast, each child was given 10 mg/kg body weight [1,1,1-13C]tripalmitin with a standardised test meal of low natural 13C abundance. The total enrichment of 13C was measured using isotope ratio mass spectrometry in stool collected for a period of up to five days and in breath samples collected over a 24 hour period. RESULTS The mean proportion of administered 13C label excreted in stool was 6% (range, 1-12.7%) in healthy children and 24.6% (range, 0-64%) in patients with cystic fibrosis. Healthy children excreted 31.3% of the administered label on their breath (range, 14.2-42.9%). Correcting the excretion of administered 13C label on the breath for differences in digestion and absorption in patients with cystic fibrosis increased the difference between individuals from 0-31.3% of administered dose (mean, 17.9%) to 0-49.1% of absorbed dose (mean, 23.2%) and was poorly related to the amount of 13C label in stool. CONCLUSION Measurements of breath 13CO2 do not consistently reflect the gastrointestinal handling of emulsified 13C labelled tripalmitin because of differences in digestion and absorption in cystic fibrosis. Further studies need to examine whether "breath tests" alone can predict with confidence the gastrointestinal handling of other 13C labelled triglycerides and fatty acids.