title: New data on the intraindividual variation of cystatin C.
abstract: BACKGROUND
  Cystatin C is a new interesting marker of glomerular filtration rate (GFR). However, data regarding its biological variance are scarce and conflicting. The ability of cystatin C to longitudinally follow renal function in patients therefore remains questionable.
  
  
  METHODS
  12 healthy subjects (6 men and 6 women) were included in the final statistical analysis. Serum creatinine, plasma cystatin C and GFR were measured twice after a 1-week interval on the same day, at the same time, and under the same preanalytical and analytical conditions. GFR was measured with an iohexol method. Serum creatinine was measured with a compensated Jaffé and an enzymatic method. Plasma cystatin C was measured by a particle-enhanced immunonephelometric method. Analytical (CV(A)) and within-subject (CV(I)) variances were classically calculated.
  
  
  RESULTS
  CV(A) for creatinine (Jaffé and enzymatic methods) and cystatin C was 2.5, 0.97 and 1.29%, respectively. CV(I) was 5.8, 5 and 4.5% for the Jaffé creatinine, enzymatic creatinine and cystatin C determinations, respectively.
  
  
  CONCLUSIONS
  Our study confirms that intraindividual variation of cystatin C and creatinine are similar. Therefore, from a biological point of view, cystatin C seems as accurate as creatinine for the longitudinal follow-up of renal function in daily clinical practice.
authors.affiliation: Department of Nephrology, University of Liege, CHU Sart Tilman, Liege, 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: Gisèle
authors.initials: G
authors.lastname: Depas
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Chapelle
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Krzesinski
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007118:Immunoassay; D007472:Iohexol; D007674:Kidney Diseases / Q000175:diagnosis* / Q000503:physiopathology; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry / Q000379:methods; D012016:Reference Values; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D007472:Iohexol; D003404:Creatinine