title: Higher extracellular fluid volume in women is concealed by scaling to body surface area.
abstract: OBJECTIVE
  The objective was to assess body surface area (BSA) for scaling extracellular fluid volume (ECV) in comparison with estimated lean body mass (LBM) and total body water (TBW) across a range of body mass indices (BMI).
  
  
  METHODS
  This was a multi-centre study from 15 centres that submitted raw data from routine measurement of GFR in potential kidney transplant donors. There were 819 men and 1059 women in total. ECV was calculated from slope-intercept and slope-only measurements of GFR. ECV was scaled using two methods: Firstly, division of ECV by the scaling variable (ratio method), and secondly the regression method of Turner and Reilly. Subjects were placed into five BMI groups: < 20, 20-24.9, 25-29.9, 30-34.9, and 35 + kg/m(2). LBM and TBW were estimated from previously published, gender-specific prediction equations.
  
  
  RESULTS
  Ratio and regression scaling gave almost identical results. ECV scaled to BSA by either method was higher in men in all BMI groups but ECV scaled to LBM and TBW was higher in women. There was, however, little difference between men and women in respect to ECV per unit weight in any BMI group, even though women have 10% more adipose tissue. The relations between TBW and BSA and between LBM and BSA, but not between LBM and TBW, were different between men and women.
  
  
  CONCLUSIONS
  Lean tissue in women contains more extracellular water than in men, a difference that is obscured by scaling to BSA. The likely problem with BSA is its insensitivity to body composition.
authors.affiliation: Department of Nuclear Medicine, Royal Sussex County Hospital , Brighton.
authors.forename: A Michael
authors.initials: AM
authors.lastname: Peters
authors.forename: Nagabhushan
authors.initials: N
authors.lastname: Seshadri
authors.forename: Mark D J
authors.initials: MD
authors.lastname: Neilly
authors.forename: Laura
authors.initials: L
authors.lastname: Perry
authors.forename: Claire A
authors.initials: CA
authors.lastname: Hooker
authors.forename: Bethany
authors.initials: B
authors.lastname: Howard
authors.forename: Ravin
authors.initials: R
authors.lastname: Sobnack
authors.forename: Andrew
authors.initials: A
authors.lastname: Irwin
authors.forename: Surendra
authors.initials: S
authors.lastname: Dave
authors.forename: Hayley
authors.initials: H
authors.lastname: Snelling
authors.forename: Thomas
authors.initials: T
authors.lastname: Gruning
authors.forename: Neva H
authors.initials: NH
authors.lastname: Patel
authors.forename: Gregory
authors.initials: G
authors.lastname: Shabo
authors.forename: Nigel
authors.initials: N
authors.lastname: Williams
authors.forename: Mark C
authors.initials: MC
authors.lastname: Barnfield
authors.forename: Richard S
authors.initials: RS
authors.lastname: Lawson
mesh_terms: D000328:Adult; D000465:Algorithms; D001823:Body Composition; D015992:Body Mass Index; D001830:Body Surface Area; D001835:Body Weight; D045604:Extracellular Fluid / Q000378:metabolism*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D016030:Kidney Transplantation; D019520:Living Donors; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012727:Sex Characteristics