Stable Isotope Technology

Stable isotope-labeled compounds are chemically and physically identical to their nonlabeled structures, but can be analyzed by mass spectrometry due to their (slight) mass difference. Therefore, they are ideal to use as in vivo markers for biochemical pathways. Stable isotopes are already naturally present, and their levels are only temporarily elevated. Since 1935, stable isotope-labeled metabolites called tracers are used in metabolic studies. As opposed to radiolabeled tracers, the use of stable isotopes is safe, and studies can be performed in newborns, infants, and pregnant women, among others. By careful consideration of the tracer choice, it is possible to perform a wide variety of experiments that are neither limited by the possibilities in administration of the tracer nor by the variety of possible sampling pools. The latter, however, is restricted by ethical considerations in the pediatric research field. In this chapter, a number of tracer administration techniques, some modeling, and a few commonly executed experiments are discussed, along with frequently used calculations.