title: Development of a population-specific regression equation to estimate total body water in hemodialysis patients.
abstract: We have previously shown that the impedance index (height corrected resistance) is a valid and reliable correlate of total body water (TBW) in hemodialysis patients. We estimated TBW by single frequency bioelectrical impedance analysis (BIA) in 3009 in-center hemodialysis patients, and developed an ESRD-specific TBW equation from routinely available demographic and anthropometric variables. The mean +/- SD age was 60.5 +/- 15.5 years; 47% were female, 47% African-American, and 36% diabetic. Dialysis duration was 3.8 +/- 3.7 years. Mean TBW was 40.8 +/- 9.3 kg, 56 +/- 9% of body weight. A stepwise linear regression equation was fit on a two-thirds random sample, deriving significant parameter estimates for the variables age, gender, height, weight, diabetic status, weight squared, and the cross-products of age and gender, age and weight, gender and weight, and height and weight. The equation was then validated in the remaining one-third sample, and compared with TBW estimates by the Watson and Hume-Weyer formulae. TBW estimated by our equation (40.6 +/- 8.6 kg) was not significantly different from the BIA TBW (40.5 +/- 9.3 kg). In contrast, TBW estimated by the Watson (37.0 +/- 7.6 kg) and Hume-Weyer (37.9 +/- 7.7 kg) formulae underestimated TBW by a mean of 3.5 and 2.6 kg, respectively. A population-specific equation provides superior prediction of TBW in hemodialysis patients. The use of formulae developed and validated in non-uremic populations may result in underestimates of TBW in patients with ESRD, and potentially, overestimates of dialysis dose approximated by the clearance-time to TBW ratio (Kt/V).
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA. gmchertow@bics.bwh.harvard.edu
authors.forename: G M
authors.initials: GM
authors.lastname: Chertow
authors.forename: J M
authors.initials: JM
authors.lastname: Lazarus
authors.forename: N L
authors.initials: NL
authors.lastname: Lew
authors.forename: L
authors.initials: L
authors.lastname: Ma
authors.forename: E G
authors.initials: EG
authors.lastname: Lowrie
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001834:Body Water / Q000378:metabolism*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D006435:Renal Dialysis; D012737:Sex Factors