title: Measurement error in estimated GFR slopes across transplant chronic kidney disease stages.
abstract: BACKGROUND
  This study examines if transplant glomerular filtration rate (GFR) slope prediction is affected by the degree of transplant chronic kidney disease (CKDT) stage.
  
  
  METHODS
  Serial changes in estimated GFR (DeltaeGFR) by Cockcroft-Gault (CG) and Modified Diet in Renal Disease-Isotope Dilution Mass Spectrometry (MDRD-IDMS) equations were compared to simultaneous changes in isotope GFR (DeltaiGFR) in renal transplant patients who had at least four scans.
  
  
  RESULTS
  Total number of patients (iGFR scans) was 99 (772) while the corresponding numbers in CKDT stages 1-4 were 33 (103), 69 (239), 75 (316) and 37 (96), respectively. Measurement error [(DeltaeGFR - DeltaiGFR) x 100/DeltaiGFR] (median +/- IQR, interquartile range) estimated from CG and MDRD-IDMS slopes were -414.29 +/- 276.16% and -342.86 +/- 210.18% (stage 1); -350.00 +/- 301.22% and -300.00 +/- 525.00% (stage 2); -26.02 +/- 404.38% and -26.58 +/- 423.13% (stage 3); 10.26 +/- 142.18% and -76.92 +/- 145.64% (stage 4), respectively. The proportion of patients with CG measurement error < or =1-fold in stages 1 and 2 of 12 and 14.5% was significantly (p < 0.05) lower than that of 36.3 and 52.8% at stages 3 and 4, respectively. Similar measurement errors were observed for MDRD-IDMS.
  
  
  CONCLUSIONS
  Transplant GFR slope prediction is affected by the degree of renal dysfunction. Errors in slope prediction are much higher in those with better function and thus add another limitation for eGFR use in longitudinal studies on progressive graft dysfunction.
authors.affiliation: Saskatchewan Transplant Program, St. Paul's Hospital, 103 Hospital Drive, Saskatoon, SK, Canada.
authors.forename: Mohammad Akhtar
authors.initials: MA
authors.lastname: Hossain
authors.forename: Ahmad
authors.initials: A
authors.lastname: Attia
authors.forename: Ahmed
authors.initials: A
authors.lastname: Shoker
mesh_terms: D000328:Adult; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000628:therapy*; D016030:Kidney Transplantation / Q000379:methods*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D003404:Creatinine