title: New combined serum creatinine and cystatin C quadratic formula for GFR assessment in children.
abstract: OBJECTIVE
  The estimated GFR (eGFR) is important in clinical practice. To find the best formula for eGFR, this study assessed the best model of correlation between sinistrin clearance (iGFR) and the solely or combined cystatin C (CysC)- and serum creatinine (SCreat)-derived models. It also evaluated the accuracy of the combined Schwartz formula across all GFR levels.
  
  
  METHODS
  Two hundred thirty-eight iGFRs performed between January 2012 and April 2013 for 238 children were analyzed. Regression techniques were used to fit the different equations used for eGFR (i.e., logarithmic, inverse, linear, and quadratic). The performance of each model was evaluated using the Cohen κ correlation coefficient and the percentage reaching 30% accuracy was calculated.
  
  
  RESULTS
  The best model of correlation between iGFRs and CysC is linear; however, it presents a low κ coefficient (0.24) and is far below the Kidney Disease Outcomes Quality Initiative targets to be validated, with only 84% of eGFRs reaching accuracy of 30%. SCreat and iGFRs showed the best correlation in a fitted quadratic model with a κ coefficient of 0.53 and 93% accuracy. Adding CysC significantly (P<0.001) increased the κ coefficient to 0.56 and the quadratic model accuracy to 97%. Therefore, a combined SCreat and CysC quadratic formula was derived and internally validated using the cross-validation technique. This quadratic formula significantly outperformed the combined Schwartz formula, which was biased for an iGFR≥91 ml/min per 1.73 m(2).
  
  
  CONCLUSIONS
  This study allowed deriving a new combined SCreat and CysC quadratic formula that could replace the combined Schwartz formula, which is accurate only for children with moderate chronic kidney disease.
authors.affiliation: Department of Pediatrics, Division of Pediatric Nephrology, , ‡Department of Pediatrics, Division of Pediatric Surgery, and , §Central Chemistry Laboratory, Lausanne University Hospital, Lausanne Switzerland; , †CRC & Division of Clinical Epidemiology, Department of Health and Community Medicine, University of Geneva & University Hospitals of Geneva, Geneva, Switzerland, ‖Department of Pediatrics, Division of Pediatric Nephrology, Geneva University Hospital, Geneva, Switzerland.
authors.forename: Hassib
authors.initials: H
authors.lastname: Chehade
authors.forename: Francois
authors.initials: F
authors.lastname: Cachat
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Jannot
authors.forename: Blaise-Julien
authors.initials: BJ
authors.lastname: Meyrat
authors.forename: Dolores
authors.initials: D
authors.lastname: Mosig
authors.forename: Daniel
authors.initials: D
authors.lastname: Bardy
authors.forename: Paloma
authors.initials: P
authors.lastname: Parvex
authors.forename: Eric
authors.initials: E
authors.lastname: Girardin
mesh_terms: D000293:Adolescent; D000367:Age Factors; D015415:Biomarkers / Q000097:blood; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology; D015203:Reproducibility of Results; D012720:Severity of Illness Index
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D003404:Creatinine