Combining near-subject absolute and relative measures of longitudinal hydration in hemodialysis.

BACKGROUND AND OBJECTIVES: The feasibility and additional value of combining bioimpedance analysis (BIA) with near-subject absolute measurement of total body water using deuterium dilution (TBW(D)) in determining longitudinal fluid status was investigated. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Fifty-nine hemodialysis patients (17 female; age 58.4 +/- 16.1 yr; body mass index 27.0 +/- 5.4) were enrolled into a 12-mo, two-center, prospective cohort study. Deuterium concentration was measured in breath by flowing-afterglow mass spectrometry using a validated protocol ensuring full equilibration with the TBW; BIA was measured using a multifrequency, multisegmental device. Comorbidity was quantified by the Stoke score. Clinicians were blinded to body composition data.
RESULTS: At baseline and 12 mo, there was an incremental discrepancy between TBW(BIA) and TBW(D) volumes such that greater comorbidity was associated with increasing overhydration. Forty-three patients who completed the study had no longitudinal differences in the prescribed or achieved postdialysis weights. In contrast, TBW(D) increased without a change in TBW(BIA) (mean difference -0.10 L). Changes in TBW and lean body mass differed according to baseline comorbidity; without comorbidity, BIA also identified an increase in TBW and lean body mass, whereas with increasing comorbid burden, BIA failed to demonstrate increases in tissue hydration identified by TBW(D).
CONCLUSIONS: Combined near-patient measurements of absolute and BIA-estimated TBW are achievable in a dialysis facility by identifying changes in body composition not fully appreciated by routine assessment. BIA underestimates tissue overhydration that is associated with comorbidity, resulting in reduced sensitivity to longitudinal increases during a 12-mo period.