title: Modification of the Schwartz equations for children increases their accuracy at eGFR > 60 mL/min/1.73 m(2).
abstract: OBJECTIVE
  Estimation of eGFR in children with normal kidney function using the Schwartz equations results in underestimating real GFR.
  
  
  METHODS
  We propose modification of three Schwartz equations - two based on creatinine concentration (eGFRScrBS bedside) and (eGFRScr) and one 3-marker based on creatinine, urea and cystatin C concentrations (eGFRS3M). The iohexol test (reference method) was performed 417 times in 353 children >2 years with mean GFR: 98 ± 31.6 ml/min/1.73m(2). The assessment included also the Filler and Zappitelli equations. The modification was performed using methods: (1) based on equation, eGFRcor = a [eGFR - T] + T, where T = 50, if eGFR > T, and a equals for: eGFRScrBS 1.4043, for eGFRScr 2.0048, for eGFRS3M 1.2951, and (2) based on correction of all coefficients of the original equation.
  
  
  RESULTS
  For comparison of all the results and for children with GFR< 60, 60-90, 90-135 and > 135 ml/min/1.73m(2) the correlation coefficient, relative error (RE) and root mean square relative error (RMSRE) was employed and revealed improvement of RE from 25.9 to 6.8 and 3.9% (depending on the correction method) for eGFRScr; from 19 to 8.1 and 3.9% for eGFRScrBS and: from 11.6% to 2.0 and 2.3% for eGFRS3M (respectively). The RMSRE values changed from 30 to 21.3 and 19.8% for eGFRScr, from 25.1 to 21.6 and 19.8% for eGFRScrBS and from 19.1 to 15.8 and 15.3 % for eGFRS3M.
  
  
  CONCLUSIONS
  Modifications of Schwartz equations at GFR > 60 ml/min/1.73m(2) significantly improves the accuracy of calculating eGFR. The 3-markers equation is more accurate and should be employed frequently.
authors.affiliation: a Department of Pediatric Nephrology , Jagiellonian University Medical College , Kraków , Poland ;
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Zachwieja
authors.affiliation: b Faculty Computer Science, Electronics and Telecommunications , AGH University of Science and Technology , Kraków , Poland ;
authors.forename: Przemysław
authors.initials: P
authors.lastname: Korohoda
authors.affiliation: c Pediatric Nephrology Department , Children's University Hospital of Kraków , Kraków , Poland ;
authors.forename: Joanna
authors.initials: J
authors.lastname: Kwinta-Rybicka
authors.affiliation: a Department of Pediatric Nephrology , Jagiellonian University Medical College , Kraków , Poland ;
authors.forename: Monika
authors.initials: M
authors.lastname: Miklaszewska
authors.affiliation: a Department of Pediatric Nephrology , Jagiellonian University Medical College , Kraków , Poland ;
authors.forename: Anna
authors.initials: A
authors.lastname: Moczulska
authors.affiliation: d Clinical Biochemistry Department , Jagiellonian University Medical College , Kraków , Poland.
authors.forename: Jolanta
authors.initials: J
authors.lastname: Bugajska
authors.affiliation: d Clinical Biochemistry Department , Jagiellonian University Medical College , Kraków , Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Berska
authors.affiliation: a Department of Pediatric Nephrology , Jagiellonian University Medical College , Kraków , Poland ;
authors.forename: Dorota
authors.initials: D
authors.lastname: Drożdż
authors.affiliation: a Department of Pediatric Nephrology , Jagiellonian University Medical College , Kraków , Poland ;
authors.forename: Jacek A
authors.initials: JA
authors.lastname: Pietrzyk
mesh_terms: D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D061827:Dimensional Measurement Accuracy; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D008962:Models, Theoretical; D012016:Reference Values; D065667:Renal Elimination / Q000502:physiology; D015203:Reproducibility of Results; D014508:Urea / Q000097:blood*
chemical_list: D055316:Cystatin C; D014508:Urea; D003404:Creatinine
keywords: CKD; Children; GFR calculation; GFR equations; iohexol test