title: Discrepancies between creatinine-based and cystatin C-based equations in estimating prevalence of stage 3 chronic kidney disease in an elderly population.
abstract: BACKGROUND
  The prevalence of stage 3 chronic kidney disease (CKD) is increasing, calculated using the modification of diet in renal disease (MDRD) study equation for estimating glomerular filtration rate (GFR). Cystatin C-based equations are also being used to estimate GFR. Using creatinine-based and cystatin C-based equations, the aim of our study was to measure the difference in prevalence of stage 3 CKD in a population.
  
  
  METHODS
  CKD screening is organized in the Province of Liege, Belgium. On a voluntary basis, people aged between 45 and 75 years are invited for screening. GFR is estimated using the MDRD study equation and by the three recent cystatin C-based equations proposed by Levey's group. The Levey 1 equation is based on cystatin C only and the Levey 2 equation on cystatin C corrected for age and sex. The Levey 3 equation combines cystatin C, creatinine, age and sex.
  
  
  RESULTS
  The population screened comprised 754 people. Cystatin C is highly correlated with creatinine (r = 0.6196, p<0.0001). Prevalence of stage 3 CKD when GFR is estimated by the MDRD equation study is 17.2%, which is significantly and much higher than the prevalence obtained when cystatin C-based equations are used. Indeed, prevalence is 2%, 3.3% and 5.8% with the Levey 1, 2 and 3 equations, respectively.
  
  
  CONCLUSIONS
  The prevalence of stage 3 CKD varies strongly following the method used for estimating GFR, creatinine-based or cystatin C-based equations. Such discrepancies must be confirmed and explained in additional studies using GFR measured with a reference method.
authors.affiliation: Department of Nephrology, University of Liège, CHU Sart Tilman, Liège, Belgium. pierre_delanaye@yahoo.fr
authors.forename: Pierre
authors.initials: P
authors.lastname: Delanaye
authors.forename: Etienne
authors.initials: E
authors.lastname: Cavalier
authors.forename: Annie
authors.initials: A
authors.lastname: Saint-Remy
authors.forename: Laurence
authors.initials: L
authors.lastname: Lutteri
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Krzesinski
mesh_terms: D000368:Aged; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000175:diagnosis / Q000453:epidemiology*; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D015995:Prevalence
chemical_list: D055316:Cystatin C; D003404:Creatinine