WEEKLY VARIABILITY IN TOTAL-BODY WATER USING H2O-H-2 DILUTION IN COLLEGE-AGE MALES

The variability in measuring total body water (TBW) using deuterium oxide ((H2O))-H-2 dilution has not been extensively tested. The purpose of this study was to determine the variability of weekly measurements of TBW utilizing the (H2O)-H-2 dilution technique in 10 males and to determine the amount of biological versus technical variability using a generalizability ANOVA (GENOVA). Ten male subjects aged 21-32 yr were tested on four separate occasions for body weight (BW), underwater weight (U(w)W(t)) and TBW. BW remained quite stable across the four sessions with a 0.7% coefficient of variation (CV). Both U(w)W(t) and TBW had a CV of 4% across the four sessions. No differences were found between TBW estimates from plasma, saliva, or urine. GENOVA analysis determined that 25-50% of the total variability in measuring TBW was attributed to the sample analysis/separation procedures. Four percent of the TBW in these subjects was 1.81. This technique would therefore not be expected to detect changes less than 0.91 (50% of 1.81). The estimates of %FAT from TBW were lower but not significantly different from U(w)W(t). Blood, urine, and saliva were able to produce similarly repeatable measures of TBW.