title: Estimating glomerular filtration rate in a population-based study.
abstract: BACKGROUND
  Glomerular filtration rate (GFR)-estimating equations are used to determine the prevalence of chronic kidney disease (CKD) in population-based studies. However, it has been suggested that since the commonly used GFR equations were originally developed from samples of patients with CKD, they underestimate GFR in healthy populations. Few studies have made side-by-side comparisons of the effect of various estimating equations on the prevalence estimates of CKD in a general population sample.
  
  
  METHODS
  We examined a population-based sample comprising adults from Wisconsin (age, 43-86 years; 56% women). We compared the prevalence of CKD, defined as a GFR of <60 mL/min per 1.73 m(2) estimated from serum creatinine, by applying various commonly used equations including the modification of diet in renal disease (MDRD) equation, Cockcroft-Gault (CG) equation, and the Mayo equation. We compared the performance of these equations against the CKD definition of cystatin C >1.23 mg/L.
  
  
  RESULTS
  We found that the prevalence of CKD varied widely among different GFR equations. Although the prevalence of CKD was 17.2% with the MDRD equation and 16.5% with the CG equation, it was only 4.8% with the Mayo equation. Only 24% of those identified to have GFR in the range of 50-59 mL/min per 1.73 m(2) by the MDRD equation had cystatin C levels >1.23 mg/L; their mean cystatin C level was only 1 mg/L (interquartile range, 0.9-1.2 mg/L). This finding was similar for the CG equation. For the Mayo equation, 62.8% of those patients with GFR in the range of 50-59 mL/min per 1.73 m(2) had cystatin C levels >1.23 mg/L; their mean cystatin C level was 1.3 mg/L (interquartile range, 1.2-1.5 mg/L). The MDRD and CG equations showed a false-positive rate of >10%.
  
  
  CONCLUSIONS
  We found that the MDRD and CG equations, the current standard to estimate GFR, appeared to overestimate the prevalence of CKD in a general population sample.
authors: Department of Community Medicine, West Virginia University School of Medicine, Morgantown, WV 26506, USA. ashankar@hsc.wvu.edu
authors: Anoop
authors: A
authors: Shankar
authors: Kristine E
authors: KE
authors: Lee
authors: Barbara E K
authors: BE
authors: Klein
authors: Paul
authors: P
authors: Muntner
authors: Peter C
authors: PC
authors: Brazy
authors: Karen J
authors: KJ
authors: Cruickshanks
authors: F Javier
authors: FJ
authors: Nieto
authors: Lorraine G
authors: LG
authors: Danforth
authors: Carla R
authors: CR
authors: Schubert
authors: Michael Y
authors: MY
authors: Tsai
authors: Ronald
authors: R
authors: Klein
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D016001:Confidence Intervals; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D012016:Reference Values; D012494:Sampling Studies; D012737:Sex Factors; D014922:Wisconsin / Q000453:epidemiology
chemical_list: D055316:Cystatin C; D003404:Creatinine