title: Diagnostic accuracy of cystatin C-based eGFR equations at different GFR levels in children.
abstract: OBJECTIVE
  The diagnostic accuracy of cystatin C estimated GFR (eGFR) by various cystatin C equations have varied in different studies. We hypothesized that the GFR level of enrolled patients affects the diagnostic accuracy of a cystatin C equation.
  
  
  METHODS
  We analyzed 240 consecutively enrolled children at a single Canadian center in a prospective and cross-sectional study. Cystatin C was analyzed with nephelometry, and cystatin C eGFR was estimated by the equations validated in children. GFR was measured by technetium-99m-diethylene-triamine penta-acetic acid (⁹⁹m)Tc DTPA).
  
  
  RESULTS
  We compared various cystatin C equations across GFR strata < 60, < 90, ≥ 135, and ≥ 150 ml/min per 1.73 m² for an accurate prediction and appropriate classification of the measured GFR. The CKiD, Zappitelli-CysEq, and Zappitelli-CysCrEq equations had a higher accuracy, estimated by eGFR values within 10% and 30% of the respective (99m)Tc DTPA, in the GFR categories < 60 and < 90 ml/min per 1.73 m², whereas the Bökenkamp, Bouvet, and Filler equations had a greater accuracy in the GFR categories ≥ 135 and ≥ 150 ml/min per 1.73 m². The Bouvet, CKiD, Filler, Zappitelli-CysEq, and Zappitelli-CysCrEq equations had a greater sensitivity to classify GFR < 60 and < 90 ml/min per 1.73 m², whereas the Bökenkamp equation had a higher sensitivity for GFR ≥ 135 and ≥ 150 ml/min per 1.73 m².
  
  
  CONCLUSIONS
  The diagnostic accuracy of various cystatin C equations varies with GFR. This issue needs consideration while applying these equations in clinical practice and for further research on eGFR equations.
authors.affiliation: Department of Pediatrics, Division of Pediatric Nephrology, Children's Hospital, London Health Sciences Centre, University of Western Ontario, London, Ontario, N6A 5W9 Canada. guido.filler@lhsc.on.ca
authors.forename: Ajay P
authors.initials: AP
authors.lastname: Sharma
authors.forename: Abeer
authors.initials: A
authors.lastname: Yasin
authors.forename: Amit X
authors.initials: AX
authors.lastname: Garg
authors.forename: Guido
authors.initials: G
authors.lastname: Filler
mesh_terms: D000293:Adolescent; D015415:Biomarkers / Q000097:blood; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000032:analysis*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D007674:Kidney Diseases / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D008954:Models, Biological; D009864:Ontario; D011237:Predictive Value of Tests; D011379:Prognosis; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D016284:Technetium Tc 99m Pentetate
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D019275:Radiopharmaceuticals; D016284:Technetium Tc 99m Pentetate