Noninvasive Techniques for the Evaluation of Gastrointestinal Function

The study of gastrointestinal function during infancy has been impeded by the invasiveness, impracticality, and imprecision of the conventional techniques of internal medicine transposed to newborn and young infants. Quantitative data on the intraluminal phase of digestion are usually obtained in adults from analyses of duodenal fluid, whereas mucosal functions are investigated with biopsies and intestinal perfusion techniques. However, the performance of biopsy and intubation procedures is more difficult in infants, and cannot be practiced in asymptomatic infants. Noninvasive techniques for the evaluation of gastrointestinal function are, therefore, appealing to clinicians and investigators dealing with infants. This review will discuss well-established measurements using fluids obtained noninvasively: serum, urine, feces, and breath. Appropriate applications and limitations of the various methodologies will be considered, with particular emphasis on recently introduced techniques of breath analysis in the pediatric population. For purposes of discussion, techniques are organized according to the phase of digestion or absorption assessed by a particular method (Table 1).