Measuring the glomerular filtration rate in obese individuals without overt kidney disease.
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.
Friedman
Allon N
AN
Division of Nephrology, Indiana University School of Medicine, Indianapolis, Ind., USA. allfried@iupui.edu
Strother
Matthew
M
Quinney
Sara K
SK
Hall
Stephen
S
Perkins
Susan M
SM
Brizendine
Edward J
EJ
Inman
Margaret
M
Gomez
Gerardo
G
Shihabi
Zak
Z
Moe
Sharon
S
Li
Lang
L
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*
D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D007472:Iohexol; D003404:Creatinine