title: Inaccuracies in estimated glomerular filtration rate in one Australian renal centre.
abstract: BACKGROUND
  Early identification of true renal disease (glomerular filtration rate (GFR) < 60 mL/min) results in better patient outcomes. There is now routine reporting in Australia of estimated GFR (eGFR) in all patients over age 18 who have serum creatinine measured, calculated by the Modification of Diet in Renal Disease (MDRD) formula, which was validated in an American Caucasian cohort. Significant clinical decisions and prognosis are often made on the basis of this calculation.
  
  
  OBJECTIVE
  To assess the accuracy of three estimates of GFR in an Australian population by comparing eGFR obtained by the abbreviated MDRD (aMDRD), Cockcroft-Gault corrected for body surface area (BSA) (CG) and Chronic Kidney Disease Epidemiology (CKD-Epi) formulae with a gold standard, isotopic (51) Cr-ethylenediaminetetra-acetic acid ((51) Cr-EDTA) GFR.
  
  
  METHODS
  Patients referred with an eGFR of <60 mL/min reported by the aMDRD formula underwent isotopic measurement of GFR (over 4 h) and had eGFR calculated using CG corrected for BSA, aMDRD and CKD-Epi formulae. Data were analysed using Bland-Altman plots and regression analysis to compare methods; bias, precision and the proportion of patients correctly stratified by stage of chronic kidney disease (CKD) were also compared according to the three estimates of GFR, using (51) Cr-EDTA GFR as the gold standard.
  
  
  RESULTS
  A total of 139 patients were recruited (female 45%), mean age 64 years and mean serum creatinine 212 µmol/L. The mean GFR (SD) (mL/min per m(2) ) for isotopic, CG, aMDRD and CKD-Epi were 47 (28), 37 (20), 32 (17) and 33 (18) (P = 0.001). CG (57%) was more likely to correctly stage CKD than aMDRD (37%) or CKD-Epi (37%), and absolute bias was significantly lower using CG than either other method (P = 0.001).
  
  
  CONCLUSIONS
  In this small Australian population the CG formula corrected for BSA agreed more closely with isotopic GFR and correctly staged patients with CKD more often than the aMDRD or CKD-Epi formulae. It is important that each renal Unit considers the accuracy of estimates of GFR according to their population demographics.
authors.affiliation: Department of Renal Medicine, St George Hospital and University of New South Wales, Sydney, New South Wales, Australia. mbrown@unsw.edu.au
authors.forename: Mark A
authors.initials: MA
authors.lastname: Brown
authors.forename: Saiyini
authors.initials: S
authors.lastname: Pirabhahar
authors.forename: John J
authors.initials: JJ
authors.lastname: Kelly
authors.forename: George J
authors.initials: GJ
authors.lastname: Mangos
authors.forename: Callie
authors.initials: C
authors.lastname: Mackenzie
authors.forename: Peter
authors.initials: P
authors.lastname: McConachie
authors.forename: Julia
authors.initials: J
authors.lastname: Janssen
authors.forename: Richard C
authors.initials: RC
authors.lastname: Smart
mesh_terms: D000328:Adult; D000368:Aged; D001315:Australia; D004492:Edetic Acid / Q000493:pharmacokinetics; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D004369:Pentetic Acid / Q000493:pharmacokinetics
chemical_list: D004369:Pentetic Acid; D004492:Edetic Acid