Measurement of total body water in human infants using deuterium isotope dilution and nuclear magnetic resonance spectroscopy

Total body water (TBW) provides a useful measure of fat-free body mass. Deuterium (D) oxide isotope dilution is a useful method to determine TBW. Various techniques, including density, infrared absorption, mass spectrometry and gas chromatography have been employed to determine D enrichment in body fluids. Each of these methods requires extensive sample preparation (sublimation or distillation of the body fluid). The authors have employed nuclear magnetic resonance (NMR) spectroscopy to measure D enrichment in saliva and urine of human infants. No sample preparation was necessary. A standard (dg-t-butanol) was added to 0.5 ml of sample and D enrichment was measured using a JEOL FX-900 NMR spectrometer. Signal acquisition time was 4.7 min. Working range of D enrichment was 0.04-0.32 atom % D (corresponding to an oral dose of approximately 0.25-2.0 g D2O/kg body weight). Coefficients of variation (c.v.) for saliva samples at 0.20 and 0.06 atom % enrichment were 1.97% and 4.78%, respectively. Mean (+/-SD) of TBW determinations for 6 infants was 58.5 +/- 5.4% of body weight (range 53-66%). Repeat measurements (3) of TBW for each infant at weekly intervals yielded a mean c.v. of 4.1% (n = 6). This method provides precise measurement of TBW without the extensive sample preparation requirements of previously-described methods