title: Kidney function estimating equations in patients with chronic kidney disease.
abstract: BACKGROUND
  The current guidelines emphasise the need to assess kidney function using predictive equations rather than just serum creatinine. The present study compares serum cystatin C-based equations and serum creatinine-based equations in patients with chronic kidney disease (CKD).
  
  
  METHODS
  Seven hundred and sixty-four adult patients with CKD were enrolled. In each patient serum creatinine and serum cystatin C were determined. Their glomerular filtration rate (GFR) was estimated using three serum creatinine-based equations [Cockcroft-Gault (C&G), modification of diet in renal disease (MDRD) and the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI)] and two serum cystatin C-based equations [our own cystatin C formula (GFR=90.63 × cystatin C(-1.192) ) and simple cystatin C formula (GFR=100/cystatin C)]. The GFR was measured using (51) CrEDTA clearance.
  
  
  RESULTS
  Statistically significant correlation between (51) CrEDTA clearance with serum creatinine, serum cystatin C and all observed formulas was found. The receiver operating characteristic curve analysis (cut-off for GFR 60 ml/min/1.73m(2)) showed that serum cystatin C and both cystatin C formulas had a higher diagnostic accuracy than C&G formula. Bland and Altman analysis for the same cut-off value showed that all formulas except simple cystatin C formula underestimated measured GFR. The accuracy within 30% of estimated (51) CrEDTA clearance values differs according to stages of CKD. Analysis of ability to correctly predict patient's GFR below or above 60 ml/min/1.73m(2) showed statistically significant higher ability for both cystatin C formulas compared to MDRD formula.
  
  
  CONCLUSIONS
  Our results indicate that serum cystatin C-based equations are reliable markers of GFR comparable with creatinine-based formulas.
authors.affiliation: Department of Nephrology, Clinic of Internal Medicine, University Medical center Maribor, Maribor, Slovenia.
authors.forename: R
authors.initials: R
authors.lastname: Hojs
authors.forename: S
authors.initials: S
authors.lastname: Bevc
authors.forename: R
authors.initials: R
authors.lastname: Ekart
authors.forename: M
authors.initials: M
authors.lastname: Gorenjak
authors.forename: L
authors.initials: L
authors.lastname: Puklavec
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D002614:Chelating Agents; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D004492:Edetic Acid; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007674:Kidney Diseases / Q000097:blood / Q000175:diagnosis / Q000503:physiopathology*; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D012372:ROC Curve; D055815:Young Adult
chemical_list: D015415:Biomarkers; D002614:Chelating Agents; D055316:Cystatin C; D004492:Edetic Acid; D003404:Creatinine