title: Impact of creatinine calibration on performance of GFR estimating equations in a pooled individual patient database.
abstract: BACKGROUND
  Variation in performance of glomerular filtration rate (GFR) estimating equations is related to variation in calibration of the creatinine assay across clinical laboratories.
  
  
  METHODS
  Cross-sectional analysis.
  
  
  METHODS
  6 research studies and 4 clinical populations including 5,504 participants who had GFR measured using urinary clearance of iothalamate.
  
  
  METHODS
  Standardized serum creatinine values obtained by means of calibration to the Cleveland Clinic Research Laboratory using frozen specimens, a calibration panel, and/or survey results from the College of American Pathologists.
  
  
  METHODS
  Noncalibrated serum creatinine assayed in research and clinical laboratories compared with standardized serum creatinine.
  
  
  RESULTS
  Difference between measured GFR versus GFR estimated from the Modification of Diet in Renal Disease (MDRD) Study and Cockcroft-Gault equations.
  
  
  RESULTS
  For a noncalibrated serum creatinine value of 1 mg/dL (88.4 micromol/L), standardized serum creatinine value was 0.07 mg/dL (6.2 micromol/L) less than noncalibrated values. In the pooled data set, for the MDRD Study equation, calibration improved median percentage of difference between measured and estimated GFR from 9.0% (interquartile range [IQR], 28%) to 5.8% (IQR, 28%) and improved the percentage of estimates within 30% of measured GFR (P30) from 80% to 83%. The effect of calibration was greater at higher levels of GFR and varied across studies. For the Cockcroft-Gault equation, calibration worsened the median percentage of difference from -2.0% (IQR, 38%) to -11.4% (IQR, 39%), and the P30, from 74% to 69%.
  
  
  CONCLUSIONS
  College of American Pathologist samples were used for calibration of clinical populations; calibration factors do not account for drift over time in the serum creatinine assay; calibration cannot account for variation in assay performance among individuals.
  
  
  CONCLUSIONS
  Calibration improves the performance of the MDRD Study equation. After calibration, larger errors remain for GFR estimates greater than 60 mL/min/1.73 m2 (>1 mL/s/1.73 m2).
authors.affiliation: Division of Nephrology, Tufts-New England Medical Center, 750 Washington St, Box #391, Boston, MA 02111, USA. lstevens1@tufts-nemc.org <lstevens1@tufts-nemc.org>
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Stevens
authors.forename: Jane
authors.initials: J
authors.lastname: Manzi
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Levey
authors.forename: Jing
authors.initials: J
authors.lastname: Chen
authors.forename: Amy E
authors.initials: AE
authors.lastname: Deysher
authors.forename: Tom
authors.initials: T
authors.lastname: Greene
authors.forename: Emilio D
authors.initials: ED
authors.lastname: Poggio
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Schmid
authors.forename: Michael W
authors.initials: MW
authors.lastname: Steffes
authors.forename: Yaping Lucy
authors.initials: YL
authors.lastname: Zhang
authors.forename: Frederick
authors.initials: F
authors.lastname: Van Lente
authors.forename: Josef
authors.initials: J
authors.lastname: Coresh
mesh_terms: D000328:Adult; D002138:Calibration; D019411:Clinical Laboratory Techniques / Q000592:standards*; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007483:Iothalamic Acid / Q000493:pharmacokinetics; D007676:Kidney Failure, Chronic / Q000097:blood / Q000503:physiopathology*; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D011786:Quality Control; D012015:Reference Standards
chemical_list: D007483:Iothalamic Acid; D003404:Creatinine