title: Understanding estimated glomerular filtration rate: implications for identifying chronic kidney disease.
abstract: OBJECTIVE
  Glomerular filtration rate (GFR) can be estimated using serum markers such as serum creatinine (SCr) or cystatin C. This review presents new insights into estimated GFR based on theory, validation studies, SCr assay standardization, cystatin C, and longitudinal comparison with measured GFR.
  
  
  RESULTS
  The estimation of GFR by SCr differs in health and in chronic kidney disease (CKD) due to differences in GFR range and in creatinine production between these two populations. Among populations with normal baseline GFR, there is a more rapid decline in measured GFR than in SCr-based estimated GFR. While elevated SCr is specific for CKD, other disease processes may lead to elevated cystatin C. Validation is improved by refitting equation coefficients to compare populations, recognizing the asymmetry between estimated GFR and measured GFR, and using residual plots instead of Bland-Altman plots to assess bias.
  
  
  CONCLUSIONS
  As a screening test, SCr should be interpreted as a marker of CKD probability in the context of the patient's clinical presentation. Measured GFR or creatinine clearance may be helpful in high-risk patients with normal SCr levels. GFR estimating equations should be reserved for patients with identified CKD. Standardized SCr and cystatin C assays are needed.
authors.affiliation: Division of Nephrology, Mayo Clinic, Rochester, Minnesota, USA. rule.andrew@mayo.edu
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Rule
mesh_terms: D015415:Biomarkers / Q000097:blood*; D002318:Cardiovascular Diseases / Q000097:blood / Q000175:diagnosis; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood; D055316:Cystatin C; D015891:Cystatins / Q000097:blood; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology; D007677:Kidney Function Tests / Q000379:methods; D008403:Mass Screening / Q000379:methods* / Q000592:standards; D008954:Models, Biological; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D003404:Creatinine