Clinical applications of 13CO2 measurements.

The metabolism of 13C-labeled substrates to CO2 and the measurement of the appearance of excess 13C in respiratory CO2 can be used as probes for a variety of gastrointestinal and physiological functions as well as estimation of in vivo enzyme levels. These breath tests, being both nonradioactive and noninvasive, are applicable to any population of subjects, and do not require hospitalization of metabolic ward conditions for their use. They are ideally suited for assessment of nutritional status in free-living individuals once they have been validated against known dietary intake conditions.