title: Measuring the glomerular filtration rate in obese individuals without overt kidney disease.
abstract: BACKGROUND
  Identifying methods to accurately measure the glomerular filtration rate (GFR) in obese individuals without kidney overt kidney disease is necessary to understanding the pathophysiology and natural history of obesity-related kidney disease.
  
  
  METHODS
  Using a cross-sectional design, iohexol clearance and disposition was measured, an optimal sampling schedule was identified, and the reliability of GFR-estimating methods was described in 29 obese individuals with normal serum creatinine levels. Iohexol disposition was measured using population pharmacokinetics. The agreement with GFR-estimating equations was assessed by intraclass coefficients.
  
  
  RESULTS
  Mean age was 44 ± 10 years, body mass index 45 ± 10, creatinine 0.7 ± 0.2 mg/dl (62 ± 18 μmol/l) , and cystatin C 0.83 ± 0.18 mg/dl (8.3 ± 1.8 mg/l). Iohexol disposition fit a two-compartment model and 5 sampling windows were identified over a 4-hour period to optimize model accuracy and minimize blood draws. Precision was not compromised with this sampling design. Neither creatinine nor cystatin C were linearly correlated with the measured GFR though cystatin C was independent of body composition. Agreement was fair to poor between the measured GFR and GFR-estimating equations.
  
  
  CONCLUSIONS
  This study offers a rigorous method to study obesity-related kidney disease and improve upon suboptimal GFR-estimating methods.
authors.affiliation: Division of Nephrology, Indiana University School of Medicine, Indianapolis, Ind., USA. allfried@iupui.edu
authors.forename: Allon N
authors.initials: AN
authors.lastname: Friedman
authors.forename: Matthew
authors.initials: M
authors.lastname: Strother
authors.forename: Sara K
authors.initials: SK
authors.lastname: Quinney
authors.forename: Stephen
authors.initials: S
authors.lastname: Hall
authors.forename: Susan M
authors.initials: SM
authors.lastname: Perkins
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Brizendine
authors.forename: Margaret
authors.initials: M
authors.lastname: Inman
authors.forename: Gerardo
authors.initials: G
authors.lastname: Gomez
authors.forename: Zak
authors.initials: Z
authors.lastname: Shihabi
authors.forename: Sharon
authors.initials: S
authors.lastname: Moe
authors.forename: Lang
authors.initials: L
authors.lastname: Li
mesh_terms: D000328:Adult; D015415:Biomarkers; D015992:Body Mass Index; D001830:Body Surface Area; D003404:Creatinine / Q000097:blood; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol / Q000032:analysis / Q000493:pharmacokinetics; D007668:Kidney / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood / Q000503:physiopathology*
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D007472:Iohexol; D003404:Creatinine