title: Comparison of creatinine and cystatin C based eGFR in the estimation of glomerular filtration rate in Indigenous Australians: The eGFR Study.
abstract: BACKGROUND
  The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation that combines creatinine and cystatin C is superior to equations that include either measure alone in estimating glomerular filtration rate (GFR). However, whether cystatin C can provide any additional benefits in estimating GFR for Indigenous Australians, a population at high risk of end-stage kidney disease (ESKD) is unknown.
  
  
  METHODS
  Using a cross-sectional analysis from the eGFR Study of 654 Indigenous Australians at high risk of ESKD, eGFR was calculated using the CKD-EPI equations for serum creatinine (eGFRcr), cystatin C (eGFRcysC) and combined creatinine and cystatin C (eGFRcysC+cr). Reference GFR (mGFR) was determined using a non-isotopic iohexol plasma disappearance technique over 4h. Performance of each equation to mGFR was assessed by calculating bias, % bias, precision and accuracy for the total population, and according to age, sex, kidney disease, diabetes, obesity and c-reactive protein.
  
  
  RESULTS
  Data were available for 542 participants (38% men, mean [sd] age 45 [14] years). Bias was significantly greater for eGFRcysC (15.0mL/min/1.73m2; 95% CI 13.3-16.4, p<0.001) and eGFRcysC+cr (10.3; 8.8-11.5, p<0.001) compared to eGFRcr (5.4; 3.0-7.2). Accuracy was lower for eGFRcysC (80.3%; 76.7-83.5, p<0.001) but not for eGFRcysC+cr (91.9; 89.3-94.0, p=0.29) compared to eGFRcr (90.0; 87.2-92.4). Precision was comparable for all equations. The performance of eGFRcysC deteriorated across increasing levels of c-reactive protein.
  
  
  CONCLUSIONS
  Cystatin C based eGFR equations may not perform well in populations with high levels of chronic inflammation. CKD-EPI eGFR based on serum creatinine remains the preferred equation in Indigenous Australians.
authors.affiliation: Menzies School of Health Research, Darwin, Australia; Baker IDI Heart and Diabetes Institute, Melbourne, Australia. Electronic address: Elizabeth.Barr@menzies.edu.au.
authors.forename: Elizabeth Lm
authors.initials: EL
authors.lastname: Barr
authors.affiliation: Menzies School of Health Research, Darwin, Australia; Division of Medicine, Royal Darwin Hospital, Australia.
authors.forename: Louise J
authors.initials: LJ
authors.lastname: Maple-Brown
authors.affiliation: Menzies School of Health Research, Darwin, Australia.
authors.forename: Federica
authors.initials: F
authors.lastname: Barzi
authors.affiliation: Menzies School of Health Research, Darwin, Australia; Division of Medicine, Royal Darwin Hospital, Australia.
authors.forename: Jaquelyne T
authors.initials: JT
authors.lastname: Hughes
authors.affiliation: Austin Health, Melbourne, Australia; University of Melbourne, Melbourne, Australia.
authors.forename: George
authors.initials: G
authors.lastname: Jerums
authors.affiliation: Menzies School of Health Research, Darwin, Australia; Austin Health, Melbourne, Australia; University of Melbourne, Melbourne, Australia.
authors.forename: Elif I
authors.initials: EI
authors.lastname: Ekinci
authors.affiliation: Austin Health, Melbourne, Australia; University of Melbourne, Melbourne, Australia.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Ellis
authors.affiliation: SydPath, St Vincent's Hospital, Sydney, Australia; University of New South Wales, Sydney, Australia.
authors.forename: Graham Rd
authors.initials: GR
authors.lastname: Jones
authors.affiliation: Menzies School of Health Research, Darwin, Australia.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Lawton
authors.affiliation: Northern Territory Renal Services, Darwin, Australia; Northern Territory Department of Health, Darwin, Australia.
authors.forename: Cherian
authors.initials: C
authors.lastname: Sajiv
authors.affiliation: Division of Medicine, Royal Darwin Hospital, Australia; Division of Nephrology, Royal Darwin Hospital, Australia.
authors.forename: Sandawana W
authors.initials: SW
authors.lastname: Majoni
authors.affiliation: South Australian Health and Medical Research Institute, Adelaide, Australia; University of South Australia, Adelaide, Australia.
authors.forename: Alex Dh
authors.initials: AD
authors.lastname: Brown
authors.affiliation: University of Queensland, Brisbane, Australia.
authors.forename: Wendy E
authors.initials: WE
authors.lastname: Hoy
authors.affiliation: University of South Australia, Adelaide, Australia.
authors.forename: Kerin
authors.initials: K
authors.lastname: O'Dea
authors.affiliation: Menzies School of Health Research, Darwin, Australia.
authors.forename: Alan
authors.initials: A
authors.lastname: Cass
authors.affiliation: St Vincent's Hospital Melbourne, Melbourne, Australia.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: MacIsaac
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D001315:Australia / Q000453:epidemiology; D002097:C-Reactive Protein / Q000378:metabolism; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D044382:Population Groups; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D055815:Young Adult
chemical_list: D055316:Cystatin C; D002097:C-Reactive Protein; D003404:Creatinine
keywords: CKD-EPI equation; Creatinine; Cystatin C; GFR; Indigenous