PRECISION OF DLW ENERGY-EXPENDITURE MEASUREMENTS - CONTRIBUTION OF NATURAL-ABUNDANCE VARIATIONS

Accuracy and precision of the the doubly labeled water (DLW) measureme nts of energy expenditure are commonly estimated with models that do n ot account for H-2 and O-18 natural abundance variation. A new and sim ple treatment that completes the ratio-product model is derived in the present study. It uses both linear regression of multipoint data with time and information on within-subject H-2 and O-18 natural abundance variation. Use of this treatment is demonstrated in a group of seven subjects in whom H-2 and O-18 natural abundance variation was assessed by collecting predose samples for 6-8 days before dosing. In this set of 16 measurements, the precision (coefficient of variation) of indiv idual DLW estimates of CO2 production was 4.90 +/- 2.14%, of which 3.2 3 +/- 1.20% arose from natural abundance variation.