title: Body mass does not have a clinically relevant effect on cystatin C eGFR in children.
abstract: BACKGROUND
  Unlike creatinine, Cystatin C (CysC) is believed to be independent of body composition in both adults and children. Recent findings in adults, suggesting an improved performance of CysC-based estimated glomerular filtration rate (CysC eGFR) by accounting for body mass, necessitated a careful re-evaluation of this issue in children.
  
  
  METHODS
  We studied 240 children (median age 11.7 years, range 2-17.9 years, 107 girls), with various kidney diseases, for any change in the relationship between (99)Tc DTPA GFR and CysC eGFR after accounting for body mass. For body mass assessment, body mass index (BMI) z-score was calculated using height-adjusted age, to account for growth retardation secondary to chronic kidney disease.
  
  
  RESULTS
  CysC eGFR did not have a significant correlation with BMI z-score (correlation coefficient = 0.06; P = 0.34). Accounting for BMI z-score did not add to the 65% variance in nuclear GFR explained by CysC eGFR. Moreover, it did not change the regression coefficient of 0.85 between CysC eGFR and nuclear GFR either. On Bland & Altman analysis, the bias of 0.05 and standard deviation of 20.39 also did not improve after accounting for BMI z-score in the revised CysC eGFR formula.
  
  
  CONCLUSIONS
  In children, body mass exerts a minimal effect on the performance of CysC eGFR estimation.
authors.affiliation: Department of Paediatrics, Division of Paediatric Nephrology, Children's Hospital, London Health Science Centre, University of Western Ontario, London, Canada.
authors.forename: Ajay P
authors.initials: AP
authors.lastname: Sharma
authors.forename: Anusha
authors.initials: A
authors.lastname: Kathiravelu
authors.forename: Renisha
authors.initials: R
authors.lastname: Nadarajah
authors.forename: Abeer
authors.initials: A
authors.lastname: Yasin
authors.forename: Guido
authors.initials: G
authors.lastname: Filler
mesh_terms: D000293:Adolescent; D015415:Biomarkers / Q000378:metabolism; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D055316:Cystatin C / Q000378:metabolism*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007674:Kidney Diseases / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D008297:Male; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D016284:Technetium Tc 99m Pentetate
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D019275:Radiopharmaceuticals; D016284:Technetium Tc 99m Pentetate