Validation of the deuterium oxide method for measuring average daily milk intake in infants

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Abstract
The deuterium oxide elimination method for measuring average daily milk intake was validated against measured formula intake in 16 studies of 11 infants in a metabolic ward. Deuterium oxide (approximately 0.10 g/kg body wt) was given orally. Deuterium enrichment was measured in urine samples collected predose, as available for 6-h postdose for TBW determination, and at 24 h and 5–10 d postdose for HDO elimination calculated according to the two-point method. Urine samples were vacuum distilled, water was reduced to hydrogen gas, and deuterium enrichment was measured by isotope-ratio mass spectrometry. Milk intake was measured throughout the elimination period from prefeeding and postfeeding bottle weights (n = 12) or volumes (n = 4). Without corrections for atmospheric water influx, milk intake was overestimated by 76 g/d (6%). With corrections for estimated metabolic water production, isotopic fractionation, and atmospheric water influx, deuterium measured 98% +/- 3% or 1300 g milk intake/d compared with actual milk intake of 1329 +/- 206 g/d.