Analytic requirements for the doubly labeled water method.

The doubly labeled water method is the first method that accurately measures total daily energy expenditure in free-living subjects over periods of days to weeks. Validations have indicated that the method can be performed with a coefficient of variation of between 3% and 5%. This precision, however, is dependent on the quality of the isotopic analyses. A recent interlaboratory comparison has indicated that there is a wide variation in the accuracy and precision with which deuterium and 18O enrichments are measured. This reduces the accuracy and precision with which a laboratory will perform the doubly labeled water method and in some cases may limit the application of this technique. Herein we review the analytical requirements for optimal use of the method and some of the potential sources of error in the stable isotope analysis.