title: GFR estimates using cystatin C are superior to serum creatinine in adult patients with cystic fibrosis.
abstract: BACKGROUND
  Accurate assessment of renal function in patients with cystic fibrosis (CF) is vital for determining the appropriate dose of medications and for early detection of renal disease. Cystatin C (CysC) is a new marker of GFR with reportedly improved accuracy and precision compared to methods incorporating serum creatinine. The purpose of this study is to evaluate the predictive performance of cystatin C in estimating GFR in adult patients with CF.
  
  
  METHODS
  Iothalamate was administered to enable measurement of GFR in 38 adult patients with CF and control subjects. Creatinine clearance (C&G) and GFR estimates (cystatin C clearance [Cys C] and abbreviated modified diet in renal disease [aMDRD]) were compared using Bland-Altman and receiver operating characteristic (ROC) analysis. GFR cutoff values of 80 and 90 mL/min-1.73 m(2) were used in the analysis.
  
  
  RESULTS
  The measured GFR was similar in both the CF and healthy volunteers 104 (32.2) and 105 (29.9), P=0.969 respectively. No significant difference in mean bias was noted between the predictive methods within the CF population. Cys C provided the most precise estimates of GFR in both populations. ROC curves demonstrated that CysC provided greater sensitivity and specificity compared to the aMDRD (AUC 0.93 vs. 0.54, P=0.003) and C&G (AUC 0.93 vs. 0.56, P=0.005) in CF at a cutoff GFR of 90 mL/min-1.73 m(2).
  
  
  CONCLUSIONS
  Cystatin C clearance provides an improved marker of glomerular filtration rate in CF patients.
authors.affiliation: Department of Pharmacy, University of Southern California, Los Angeles, CA 90033, USA. beringer@usc.edu
authors.forename: Paul M
authors.initials: PM
authors.lastname: Beringer
authors.forename: Levita
authors.initials: L
authors.lastname: Hidayat
authors.forename: Anna
authors.initials: A
authors.lastname: Heed
authors.forename: Ling
authors.initials: L
authors.lastname: Zheng
authors.forename: Heather
authors.initials: H
authors.lastname: Owens
authors.forename: Debbie
authors.initials: D
authors.lastname: Benitez
authors.forename: Adupa P
authors.initials: AP
authors.lastname: Rao
mesh_terms: D015415:Biomarkers / Q000097:blood; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D003550:Cystic Fibrosis / Q000097:blood* / Q000150:complications; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007483:Iothalamic Acid; D007674:Kidney Diseases / Q000097:blood* / Q000150:complications / Q000175:diagnosis*; D008297:Male; D012372:ROC Curve; D055815:Young Adult
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D007483:Iothalamic Acid; D003404:Creatinine