title: Comparison of bioimpedance methods for estimating total body water and intracellular water changes during hemodialysis.
abstract: BACKGROUND
  The accurate assessment of body fluid volume is important in many clinical situations. Hannan et al. proposed a single-frequency bioimpedance equation (HE) to calculate extracellular water (ECW) and total body water (TBW). There are two equations based on the bioimpedance spectroscopy (BIS) method for the evaluation of body fluid volume: Xitron equations (XE) and body composition spectroscopy equations (BCSE). The aim of the study was to compare the accuracy of these three equations in body fluid volume point estimation in maintenance hemodialysis (MHD) patients.
  
  
  METHODS
  The BIS method was performed in MHD patients before and after a hemodialysis (HD) session. TBW, ECW and intracellular water (ICW) were calculated by XE, BCSE and HE, respectively. Hydration status (HS) was calculated using inputs of XE, BCSE and HE. ICW before dialysis was compared to ICW after dialysis. The change of TBW and HS using different equations was compared to actual ultrafiltration volume (AUV) that was calculated as weight difference of pre- to postdialysis.
  
  
  RESULTS
  Fifty MHD patients (27 females) were included in the study. Significant changes in ICW were observed using the XE and HE method with ultrafiltration (XE: 15.51 ± 5.07 versus 16.17 ± 5.34 L, P < 0.01; HE: 17.40 ± 5.13 versus 16.55 ± 4.71 L, P < 0.01). However, no significant ICW change was observed using BCSE (17.47 ± 4.35 versus 17.54 ± 4.36 L, P > 0.05). ΔTBW_XE and ΔTBW_HE were significantly different from AUV (XE 1.76 ± 0.89 versus 2.46 ± 0.89 L, P < 0.01; HE 4.16 ± 1.36 versus 2.46 ± 0.89 L, P < 0.01); however, ΔTBW_BCSE was much closer to AUV (2.27 ± 0.90 versus 2.46 ± 0.89 L, P = 0.129). The change of HS using inputs of BCSE was also closer to AUV (2.41 ± 0.86 versus 2.46 ± 0.89 L, P = 1.0).
  
  
  CONCLUSIONS
  Our study indicated that BCSE provided a better point estimation of ICW and TBW.
authors.affiliation: Renal Division, Department of Medicine, Peking University First Hospital, Beijing, People's Republic of China.
authors.forename: Yanna
authors.initials: Y
authors.lastname: Dou
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.forename: Xuyang
authors.initials: X
authors.lastname: Cheng
authors.forename: Liyun
authors.initials: L
authors.lastname: Cao
authors.forename: Li
authors.initials: L
authors.lastname: Zuo
mesh_terms: D058186:Acute Kidney Injury / Q000503:physiopathology* / Q000628:therapy*; D000465:Algorithms; D001834:Body Water; D017097:Electric Impedance; D045604:Extracellular Fluid; D005260:Female; D006801:Humans; D007424:Intracellular Fluid; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D006435:Renal Dialysis; D012307:Risk Factors; D014462:Ultrafiltration; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water