title: A comparison of change in measured and estimated glomerular filtration rate in patients with nondiabetic kidney disease.
abstract: OBJECTIVE
  All glomerular filtration rate (GFR) estimating equations have been developed from cross-sectional data. The aims of this study were to examine the concordance between use of measured GFR (mGFR) and estimated GFR (eGFR) in tracking changes in kidney function over time among patients with moderately severe chronic kidney disease.
  
  
  METHODS
  A retrospective cohort study of subjects who had been enrolled in the MDRD Study A and who had two or more contemporaneous assessments of mGFR and eGFR (n = 542; mGFR range, 25 to 55 ml/min per 1.73 m(2)) during the chronic phase (month 4 and afterwards). mGFR was based on urinary iothalamate clearance; eGFR was based on the 4-variable MDRD Study equation. Temporal changes in GFR were assessed by within-subject linear regression of time on GFR.
  
  
  RESULTS
  Median follow-up time for all subjects was 2.6 yr; median number of GFR measurements was six. The eGFR slope tended to underestimate measured decrements in GFR. The absolute value of the difference in mGFR and eGFR slopes was <or=2 ml/min per 1.73 m(2) per yr among 58.3% of subjects; the remainder of subjects had larger absolute differences. Among the 22 variables studied, none predicted a systematic difference between mGFR slope and eGFR slope.
  
  
  CONCLUSIONS
  Although eGFR and mGFR exhibited similar relationships to 22 baseline variables, the overall bias seen in the full cohort suggests that clinicians and researchers should exercise caution when interpreting eGFR slope as a marker of progression of kidney disease.
authors.affiliation: Center for Clinical Epidemiology and Biostatistics, Philadelphia, PA 19104, USA.
authors.forename: Dawei
authors.initials: D
authors.lastname: Xie
authors.forename: Marshall M
authors.initials: MM
authors.lastname: Joffe
authors.forename: Steven M
authors.initials: SM
authors.lastname: Brunelli
authors.forename: Gerald
authors.initials: G
authors.lastname: Beck
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Chertow
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Fink
authors.forename: Tom
authors.initials: T
authors.lastname: Greene
authors.forename: Chi-yuan
authors.initials: CY
authors.lastname: Hsu
authors.forename: John W
authors.initials: JW
authors.lastname: Kusek
authors.forename: Richard
authors.initials: R
authors.lastname: Landis
authors.forename: James
authors.initials: J
authors.lastname: Lash
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Levey
authors.forename: Andrew
authors.initials: A
authors.lastname: O'Conner
authors.forename: Akinlolu
authors.initials: A
authors.lastname: Ojo
authors.forename: Mahboob
authors.initials: M
authors.lastname: Rahman
authors.forename: Raymond R
authors.initials: RR
authors.lastname: Townsend
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.forename: Harold I
authors.initials: HI
authors.lastname: Feldman
mesh_terms: D000328:Adult; D018450:Disease Progression; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007483:Iothalamic Acid; D007668:Kidney / Q000503:physiopathology*; D007674:Kidney Diseases / Q000175:diagnosis* / Q000503:physiopathology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013997:Time Factors
chemical_list: D007483:Iothalamic Acid