title: Normalization of glomerular filtration rate in obese children.
abstract: Glomerular filtration rate (GFR) is conventionally indexed to body surface area (BSA), but this may lead to biased results when applied to subjects of abnormal body size. The aim of our study was to examine the impact of normalization to the BSA and alternative body size descriptors on measured and estimated GFR in overweight and obese children.
  
  
  
  This was a cross-sectional study of 313 children aged 8-9 years old. GFR was measured by 24-h creatinine clearance (CrCl) and additionally estimated from serum creatinine and cystatin C (CysC) using the combined Zappitelli formula, both as absolute values and adjusted to various body size descriptors. The results were compared between 163 normal-weight, 89 overweight and 61 obese children.
  
  
  
  Compared to the normal-weight children, mean absolute GFR (both measured and estimated) was higher in the overweight and obese children, whereas BSA-adjusted GFR was lower. Linear regression models fitted in normal-weight children revealed equally close associations between absolute GFR and squared height, ideal body weight (IBW) and BSA derived from IBW. Normalization of GFR to the IBW-derived BSA completely eliminated the discrepancy between absolute and BSA-indexed GFR in overweight and obese children.
  
  
  
  Indexing of GFR to BSA calculated from the ideal-rather than actual-body weight is a promising approach to avoid overcorrection when studying obese children. Further studies should assess the accuracy of this approach across the full range of age and BMI distribution.
authors.affiliation: Epidemiology Research Unit (EPIUnit), Institute of Public Health, University of Porto (ISPUP), Rua das Taipas nr. 135, 4050-600, Porto, Portugal. liane@med.up.pt.|Division of Pediatric Nephrology, Integrated Pediatric Hospital, Centro Hospitalar São João, Porto, Portugal. liane@med.up.pt.|Department of Pediatrics, Faculty of Medicine, University of Porto, Porto, Portugal. liane@med.up.pt.
authors.forename: Liane
authors.initials: L
authors.lastname: Correia-Costa
authors.affiliation: Division of Pediatric Nephrology, Center for Pediatrics and Adolescent Medicine, University of Heidelberg, Heidelberg, Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Schaefer
authors.affiliation: Epidemiology Research Unit (EPIUnit), Institute of Public Health, University of Porto (ISPUP), Rua das Taipas nr. 135, 4050-600, Porto, Portugal.|Division of Pediatric Nephrology, Integrated Pediatric Hospital, Centro Hospitalar São João, Porto, Portugal.|Department of Pediatrics, Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: Alberto Caldas
authors.initials: AC
authors.lastname: Afonso
authors.affiliation: Department of Nephrology, Centro Hospitalar São João, Porto, Portugal.
authors.forename: Manuela
authors.initials: M
authors.lastname: Bustorff
authors.affiliation: Epidemiology Research Unit (EPIUnit), Institute of Public Health, University of Porto (ISPUP), Rua das Taipas nr. 135, 4050-600, Porto, Portugal.|Department of Clinical Pathology , Centro Hospitalar São João, Porto, Portugal.|Department of Biochemistry, Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: João Tiago
authors.initials: JT
authors.lastname: Guimarães
authors.affiliation: Department of Pediatrics, Faculty of Medicine, University of Porto, Porto, Portugal.|Division of Pediatric Nutrition, Integrated Pediatric Hospital, Centro Hospitalar São João, Porto, Portugal.
authors.forename: António
authors.initials: A
authors.lastname: Guerra
authors.affiliation: Epidemiology Research Unit (EPIUnit), Institute of Public Health, University of Porto (ISPUP), Rua das Taipas nr. 135, 4050-600, Porto, Portugal.|Department of Clinical Epidemiology, Predictive Medicine and Public Health, Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: Henrique
authors.initials: H
authors.lastname: Barros
authors.affiliation: Epidemiology Research Unit (EPIUnit), Institute of Public Health, University of Porto (ISPUP), Rua das Taipas nr. 135, 4050-600, Porto, Portugal.|Department of Clinical Epidemiology, Predictive Medicine and Public Health, Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Azevedo
mesh_terms: D001830:Body Surface Area; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D009765:Obesity; D050177:Overweight
keywords: Body size; Body surface area; Children; Creatinine clearance; Glomerular filtration rate; Ideal body weight; Obesity