title: Bioelectrical impedance can be used to predict muscle mass and hence improve estimation of glomerular filtration rate in non-diabetic patients with chronic kidney disease.
abstract: BACKGROUND
  In this article (the second of two companion studies), we report whether bioelectrical impedance analysis (BIA) can be used to predict muscle mass in patients with chronic kidney disease (CKD), and whether using this predicted muscle mass can improve the estimation of glomerular filtration rate (GFR).
  
  
  METHODS
  Seventy five non-diabetic patients with CKD (mean age +/- SD, 65.1 +/- 12.0 years; mean GFR 45.9 +/- 28.8 ml/min/1.73 m2) underwent body composition analysis by dual energy X-ray absorptiometry to provide a criterion marker of skeletal muscle mass (appendicular lean mass, ALM). Validity of a published BIA equation to predict ALM was evaluated and a new BIA equation was generated (ALM(BIA)) and cross-validated by the leave-one-out procedure. Renal inulin clearance provided a criterion measure of GFR (GFR(inu)). The performance of the equation including ALM(BIA) to estimate GFR(inu) was compared with demographic variables as used in the modification of diet in renal disease (MDRD) equation, by determining bias, limits of agreement and accuracy.
  
  
  RESULTS
  The previously published BIA equation to predict ALM was not valid in these patients with CKD. In contrast, our new ALM(BIA) equation cross-validated successfully. Compared with the MDRD demographic variables, using ALM(BIA) to predict GFR(inu) improved estimation performance, showing reduced bias (4.3 vs 15.6 ml/min) and improved limits of agreement (41.1 vs 59.2 ml/min) and accuracy (69.7 vs 39.4% of patients' predicted GFR did not deviate by more than 30% of GFR(inu)).
  
  
  CONCLUSIONS
  ALM(BIA) provides a clinically obtainable and valid method to predict muscle mass in patients with CKD, and using ALM(BIA) improves the estimation of GFR(inu). Researchers developing future GFR estimation equations should consider including ALM(BIA).
authors.affiliation: School of Sport, Health and Exercise Sciences, University of Wales-Bangor, George Building, Bangor, Gwynedd, LL57 2PZ. j.h.macdonald@bangor.ac.uk
authors.forename: Jamie H
authors.initials: JH
authors.lastname: Macdonald
authors.forename: Samuele M
authors.initials: SM
authors.lastname: Marcora
authors.forename: Mahdi
authors.initials: M
authors.lastname: Jibani
authors.forename: Gareth
authors.initials: G
authors.lastname: Roberts
authors.forename: Mick John
authors.initials: MJ
authors.lastname: Kumwenda
authors.forename: Ruth
authors.initials: R
authors.lastname: Glover
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Barron
authors.forename: Andrew Bruce
authors.initials: AB
authors.lastname: Lemmey
mesh_terms: D000368:Aged; D002908:Chronic Disease; D017097:Electric Impedance; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000503:physiopathology*; D008297:Male; D008433:Mathematics; D018482:Muscle, Skeletal / Q000033:anatomy & histology*