title: Study Protocol--accurate assessment of kidney function in Indigenous Australians: aims and methods of the eGFR study.
abstract: BACKGROUND
  There is an overwhelming burden of cardiovascular disease, type 2 diabetes and chronic kidney disease among Indigenous Australians. In this high risk population, it is vital that we are able to measure accurately kidney function. Glomerular filtration rate is the best overall marker of kidney function. However, differences in body build and body composition between Indigenous and non-Indigenous Australians suggest that creatinine-based estimates of glomerular filtration rate derived for European populations may not be appropriate for Indigenous Australians. The burden of kidney disease is borne disproportionately by Indigenous Australians in central and northern Australia, and there is significant heterogeneity in body build and composition within and amongst these groups. This heterogeneity might differentially affect the accuracy of estimation of glomerular filtration rate between different Indigenous groups. By assessing kidney function in Indigenous Australians from Northern Queensland, Northern Territory and Western Australia, we aim to determine a validated and practical measure of glomerular filtration rate suitable for use in all Indigenous Australians.
  
  
  METHODS
  A cross-sectional study of Indigenous Australian adults (target n = 600, 50% male) across 4 sites: Top End, Northern Territory; Central Australia; Far North Queensland and Western Australia. The reference measure of glomerular filtration rate was the plasma disappearance rate of iohexol over 4 hours. We will compare the accuracy of the following glomerular filtration rate measures with the reference measure: Modification of Diet in Renal Disease 4-variable formula, Chronic Kidney Disease Epidemiology Collaboration equation, Cockcroft-Gault formula and cystatin C- derived estimates. Detailed assessment of body build and composition was performed using anthropometric measurements, skinfold thicknesses, bioelectrical impedance and a sub-study used dual-energy X-ray absorptiometry. A questionnaire was performed for socio-economic status and medical history.
  
  
  CONCLUSIONS
  We have successfully managed several operational challenges within this multi-centre complex clinical research project performed across remote North, Western and Central Australia. It seems unlikely that a single correction factor (similar to that for African-Americans) to the equation for estimated glomerular filtration rate will prove appropriate or practical for Indigenous Australians. However, it may be that a modification of the equation in Indigenous Australians would be to include a measure of fat-free mass.
authors.affiliation: Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia. louise.maple-brown@menzies.edu.au
authors.forename: Louise J
authors.initials: LJ
authors.lastname: Maple-Brown
authors.forename: Paul D
authors.initials: PD
authors.lastname: Lawton
authors.forename: Jaquelyne T
authors.initials: JT
authors.lastname: Hughes
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Sharma
authors.forename: Graham Rd
authors.initials: GR
authors.lastname: Jones
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Ellis
authors.forename: Wendy
authors.initials: W
authors.lastname: Hoy
authors.forename: Alan
authors.initials: A
authors.lastname: Cass
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Macisaac
authors.forename: Ashim K
authors.initials: AK
authors.lastname: Sinha
authors.forename: Mark Ab
authors.initials: MA
authors.lastname: Thomas
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Piers
authors.forename: Leigh C
authors.initials: LC
authors.lastname: Ward
authors.forename: Katrina
authors.initials: K
authors.lastname: Drabsch
authors.forename: Sianna
authors.initials: S
authors.lastname: Panagiotopoulos
authors.forename: Robyn
authors.initials: R
authors.lastname: McDermott
authors.forename: Kevin
authors.initials: K
authors.lastname: Warr
authors.forename: Sajiv
authors.initials: S
authors.lastname: Cherian
authors.forename: Alex
authors.initials: A
authors.lastname: Brown
authors.forename: George
authors.initials: G
authors.lastname: Jerums
authors.forename: Kerin
authors.initials: K
authors.lastname: O'Dea
mesh_terms: D000328:Adult; D001315:Australia; D001823:Body Composition; D049628:Body Size; D003287:Contrast Media / Q000493:pharmacokinetics; D003430:Cross-Sectional Studies; D016208:Databases, Factual; D005260:Female; D005919:Glomerular Filtration Rate; D006303:Health Services, Indigenous / Q000592:standards*; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics; D007668:Kidney / Q000502:physiology*; D007674:Kidney Diseases / Q000175:diagnosis*; D007677:Kidney Function Tests / Q000379:methods / Q000592:standards*; D008297:Male; D011237:Predictive Value of Tests; D018570:Risk Assessment
chemical_list: D003287:Contrast Media; D007472:Iohexol