Comparative measurements of total body water in healthy volunteers by online breath deuterium measurement and other near-subject methods.
BACKGROUND
We developed a new near-subject approach, using flowing afterglow-mass spectrometry (FA-MS) and deuterium dilution, which enables the immediate measurement of total body water (TBW) from single exhalations.


OBJECTIVE
The objectives were to show the efficacy of the new FA-MS method in measuring TBW in healthy subjects and to compare these measurements with values derived from multifrequency bioelectrical impedance analysis, skinfold-thickness (SFT) measurements, and both recent and historical published regression equations.


METHODS
After baseline measurement of breath deuterium abundance, 24 healthy subjects ingested 0.3 g D(2)O/kg body wt. A second breath sample was taken after 3 h to measure the increase in deuterium, from which TBW was calculated. Bioelectrical impedance analysis was carried out with a multifrequency analyzer, and SFT was measured by a single trained observer. Methods were compared with the use of Pearson's correlation coefficient and Bland-Altman analyses.


RESULTS
TBW measures obtained by all methods were highly correlated (r = 0.95-0.98, P < 0.001), especially those between FA-MS, SFT measurement, and recent regression equations. The mean values obtained were within 2% of those published for age-matched control subjects and varied by 1-6% when all methods were compared. Systematic bias was greatest when FA-MS was compared with bioelectrical impedance analysis, which tended to underestimate TBW in smaller, female subjects. No bias related to subject size was observed in a comparison of FA-MS with SFT measurement or with more recent regression equations.


CONCLUSIONS
FA-MS is a simple and effective new approach to TBW measurement in healthy subjects. The difficulty of using population-derived equations to estimate TBW in individual subjects is emphasized.
Smith
David
D
Centre for Science and Technology in Medicine, School of Postgraduate Medicine, Keele University, Stoke-on-Trent, United Kingdom.
Engel
Barbara
B
Diskin
Ann M
AM
Spanel
Patrik
P
Davies
Simon J
SJ
D000328:Adult; D000368:Aged; D015982:Bias; D001823:Body Composition; D001824:Body Constitution; D001834:Body Water; D001944:Breath Tests; D003903:Deuterium / Q000032:analysis*; D017097:Electric Impedance; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D012680:Sensitivity and Specificity; D012727:Sex Characteristics; D012885:Skinfold Thickness
D003903:Deuterium