title: Comparison of the Schwartz and CKD-EPI Equations for Estimating Glomerular Filtration Rate in Children, Adolescents, and Adults: A Retrospective Cross-Sectional Study.
abstract: BACKGROUND
  Estimating kidney glomerular filtration rate (GFR) is of utmost importance in many clinical conditions. However, very few studies have evaluated the performance of GFR estimating equations over all ages and degrees of kidney impairment. We evaluated the reliability of two major equations for GFR estimation, the CKD-EPI and Schwartz equations, with urinary clearance of inulin as gold standard.
  
  
  RESULTS
  The study included 10,610 participants referred to the Renal and Metabolic Function Exploration Unit of Edouard Herriot Hospital (Lyon, France). GFR was measured by urinary inulin clearance (only first measurement kept for analysis) then estimated with isotope dilution mass spectrometry (IDMS)-traceable CKD-EPI and Schwartz equations. The participants' ages ranged from 3 to 90 y, and the measured GFRs from 3 to 160 ml/min/1.73 m2. A linear mixed-effects model was used to model the bias (mean ratio of estimated GFR to measured GFR). Equation reliability was also assessed using precision (interquartile range [IQR] of the ratio) and accuracy (percentage of estimated GFRs within the 10% [P10] and 30% [P30] limits above and below the measured GFR). In the whole sample, the mean ratio with the CKD-EPI equation was significantly higher than that with the Schwartz equation (1.17 [95% CI 1.16; 1.18] versus 1.08 [95% CI 1.07; 1.09], p < 0.001, t-test). At GFR values of 60-89 ml/min/1.73 m2, the mean ratios with the Schwartz equation were closer to 1 than the mean ratios with the CKD-EPI equation whatever the age class (1.02 [95% CI 1.01; 1.03] versus 1.15 [95% CI 1.13; 1.16], p < 0.001, t-test). In young adults (18-40 y), the Schwartz equation had a better precision and was also more accurate than the CKD-EPI equation at GFR values under 60 ml/min/1.73 m2 (IQR: 0.32 [95% CI 0.28; 0.33] versus 0.40 [95% CI 0.36; 0.44]; P30: 81.4 [95% CI 78.1; 84.7] versus 63.8 [95% CI 59.7; 68.0]) and also at GFR values of 60-89 ml/min/1.73 m2. In all patients aged ≥65 y, the CKD-EPI equation performed better than the Schwartz equation (IQR: 0.33 [95% CI 0.31; 0.34] versus 0.40 [95% CI 0.38; 0.41]; P30: 77.6 [95% CI 75.7; 79.5] versus 67.5 [95% CI 65.4; 69.7], respectively). In children and adolescents (2-17 y), the Schwartz equation was superior to the CKD-EPI equation (IQR: 0.23 [95% CI 0.21; 0.24] versus 0.33 [95% CI 0.31; 0.34]; P30: 88.6 [95% CI 86.7; 90.4] versus 29.4 [95% CI 26.8; 32.0]). This study is limited by its retrospective design, single-center setting with few non-white patients, and small number of patients with severe chronic kidney disease.
  
  
  CONCLUSIONS
  The results from this study suggest that the Schwartz equation may be more reliable than the CKD-EPI equation for estimating GFR in children and adolescents and in adults with mild to moderate kidney impairment up to age 40 y.
authors.affiliation: Exploration Fonctionnelle Rénale et Métabolique, Groupement Hospitalier Est Hôpital Edouard Herriot, Hospices Civils de Lyon, Lyon, France.|Coordenação de Aperfeiçoamento do Pessoal de Nível Superior (CAPES), Brasilia, Brazil.|Programa de Pós-graduação em Medicina e Ciências da Saúde, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, Brazil.|Programa de Pós-graduação em Ciências da Saúde, Universidade de Caxias do Sul, Caxias do Sul, Brazil.|Service de Biostatistique, Hospices Civils de Lyon, Lyon, France.
authors.forename: Luciano
authors.initials: L
authors.lastname: Selistre
authors.affiliation: Service de Biostatistique, Hospices Civils de Lyon, Lyon, France.|Université de Lyon, Lyon, France.|CNRS UMR 5558, Laboratoire de Biométrie et Biologie Evolutive, Equipe Biostatistique-Santé, Villeurbanne, France.
authors.forename: Muriel
authors.initials: M
authors.lastname: Rabilloud
authors.affiliation: Université de Lyon, Lyon, France.|CNRS UMR 5558, Laboratoire de Biométrie et Biologie Evolutive, Equipe Biostatistique-Santé, Villeurbanne, France.|UMR 5305, Biologie Tissulaire et Ingénierie Thérapeutique, Université Claude Bernard, Lyon, France.|Centre de Référence des Maladies Rénales Rares, Service de Néphrologie et Rhumatologie Pédiatriques, Hospices Civils de Lyon, Lyon, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Cochat
authors.affiliation: Exploration Fonctionnelle Rénale et Métabolique, Groupement Hospitalier Est Hôpital Edouard Herriot, Hospices Civils de Lyon, Lyon, France.|Coordenação de Aperfeiçoamento do Pessoal de Nível Superior (CAPES), Brasilia, Brazil.|Programa de Pós-graduação em Ciências da Saúde, Universidade de Caxias do Sul, Caxias do Sul, Brazil.
authors.forename: Vandréa
authors.initials: V
authors.lastname: de Souza
authors.affiliation: Service de Biostatistique, Hospices Civils de Lyon, Lyon, France.|Université de Lyon, Lyon, France.|CNRS UMR 5558, Laboratoire de Biométrie et Biologie Evolutive, Equipe Biostatistique-Santé, Villeurbanne, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Iwaz
authors.affiliation: Exploration Fonctionnelle Rénale et Métabolique, Groupement Hospitalier Est Hôpital Edouard Herriot, Hospices Civils de Lyon, Lyon, France.|UMR 5305, Biologie Tissulaire et Ingénierie Thérapeutique, Université Claude Bernard, Lyon, France.|INSERM UMR 1060, Université Claude Bernard Lyon I, Lyon, France.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Lemoine
authors.affiliation: Exploration Fonctionnelle Rénale et Métabolique, Groupement Hospitalier Est Hôpital Edouard Herriot, Hospices Civils de Lyon, Lyon, France.|Laboratoire de Biochimie et Biologie Moléculaire, Groupement Hospitalier Est Hôpital Edouard Herriot, Hospices Civils de Lyon, Lyon, France.
authors.forename: Françoise
authors.initials: F
authors.lastname: Beyerle
authors.affiliation: Programa de Pós-graduação em Medicina e Ciências da Saúde, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Carlos E
authors.initials: CE
authors.lastname: Poli-de-Figueiredo
authors.affiliation: Exploration Fonctionnelle Rénale et Métabolique, Groupement Hospitalier Est Hôpital Edouard Herriot, Hospices Civils de Lyon, Lyon, France.|Université de Lyon, Lyon, France.|UMR 5305, Biologie Tissulaire et Ingénierie Thérapeutique, Université Claude Bernard, Lyon, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Dubourg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000378:metabolism; D003430:Cross-Sectional Studies; D005260:Female; D005630:Fructans / Q000378:metabolism; D005919:Glomerular Filtration Rate; D006801:Humans; D007444:Inulin / Q000652:urine; D007668:Kidney / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D008962:Models, Theoretical; D051436:Renal Insufficiency, Chronic / Q000175:diagnosis* / Q000378:metabolism; D015203:Reproducibility of Results; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D005630:Fructans; C002938:polyfructosan; D007444:Inulin; D003404:Creatinine