title: Estimation of glomerular filtration rate from serum creatinine and cystatin C in octogenarians and nonagenarians.
abstract: BACKGROUND
  Equations to estimate GFR have not been well validated in the elderly and may misclassify persons with chronic kidney disease (CKD). We measured GFR and compared the performance of the Modification of Diet in Renal Disease (MDRD), the Chronic Kidney Disease-Epidemiology Collaboration (CKD-Epi) and the Berlin Initiative Study (BIS) equations based on creatinine and/or cystatin C in octogenarians and nonagenarians.
  
  
  METHODS
  Using cross-sectional analysis we assessed 95 very elderly persons (mean 85 years) living in the community. GFR was measured by iohexol (mGFR) and compared with estimates using six equations: MDRD, CKD-Epi_creatinine, CKD-Epi_cystatin, CKD-Epi_creatinine-cystatin, BIS_creatinine and BIS_creatinine-cystatin.
  
  
  RESULTS
  Mean mGFR was 55 (range,19-86) ml/min/1.73 m(2). Bias was smaller with the CKD-Epi_creatinine-cystatin and the CKD-Epi_creatinine equations (-4.0 and 1.7 ml/min/1.73 m(2)). Accuracy (percentage of estimates within 30% of mGFR) was greater with the CKD-Epi_creatinine-cystatin, BIS_creatinine-cystatin and BIS_creatinine equations (85%, 83% and 80%, respectively). Among the creatinine-based equations, the BIS_creatinine had the greatest accuracy at mGFR < 60 ml/min/1.73 m(2) and the CKD-Epi_creatinine was superior at higher GFRs (79% and 90%, respectively). The CKD-Epi_creatinine-cystatin, BIS_creatinine-cystatin and CKD-Epi_cystatin equations yielded the greatest areas under the receiver operating characteristic curve at GFR threshold = 60 ml/min/1.73 m 2 (0.88, 0.88 and 0.87, respectively). In participants classified based on the BIS_creatinine, CKD-Epi_cystatin, or BIS_creatinine-cystatin equations, the CKD-Epi_creatinine-cystatin equation tended to improve CKD classification (net reclassification index: 12.7%, p = 0.18; 6.7%, p = 0.38; and 15.9%; p = 0.08, respectively).
  
  
  CONCLUSIONS
  GFR-estimating equations CKD-Epi_creatinine-cystatin and BIS_creatinine-cystatin showed better accuracy than other equations using creatinine or cystatin C alone in very elderly persons. The CKD-Epi_creatinine-cystatin equation appears to be advantageous in CKD classification. If cystatin C is not available, both the BIS_cr equation and the CKD-Epi_cr equation could be used, although at mGFR < 60 ml/min/1.73 m(2), the BIS_cr equation seems to be the best alternative.
authors.forename: Marcelo B
authors.initials: MB
authors.lastname: Lopes
authors.forename: Lara Q
authors.initials: LQ
authors.lastname: Araújo
authors.forename: Michelle T
authors.initials: MT
authors.lastname: Passos
authors.forename: Sonia K
authors.initials: SK
authors.lastname: Nishida
authors.forename: Gianna M
authors.initials: GM
authors.lastname: Kirsztajn
authors.forename: Maysa S
authors.initials: MS
authors.lastname: Cendoroglo
authors.affiliation: Nephrology, School of Medicine, Federal University of São Paulo, São Paulo, Brazil. rsesso@unifesp.br.
authors.forename: Ricardo C
authors.initials: RC
authors.lastname: Sesso
mesh_terms: D000369:Aged, 80 and over; D000465:Algorithms; D015415:Biomarkers / Q000097:blood; D001938:Brazil / Q000453:epidemiology; D003401:Creatine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D005260:Female; D015577:Geriatric Assessment; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D015995:Prevalence; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology*; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D003401:Creatine