title: Cystatin C as an endogenous marker of glomerular filtration rate in renal transplant patients.
abstract: BACKGROUND
  Serum creatinine is the most common endogenous marker used to estimate the glomerular filtration rate (GFR). However, creatinine depends considerably on muscle mass, and its tubular secretion increases, especially in chronic renal failure. Cystatin C is a 13-kD protease inhibitor which is produced by all nucleated cells and is independent of muscle mass and sex. Cystatin C is eliminated by glomerular filtration and metabolized by proximal tubular cells. Its measurement has been proposed as an alternative and more sensitive marker of GFR than creatinine in patients with slight to moderately decreased GFR.
  
  
  METHODS
  We investigated serum cystatin C levels in comparison with creatinine as a single measurement for estimation of GFR in 173 patients after renal transplantation. GFR was calculated as creatinine clearance according to standard equations.
  
  
  RESULTS
  Serum creatinine correlated well with cystatin C (r = 0.84; p < 0.0001). No significant differences were obtained for the comparison of the linear correlation of 1/creatinine with creatinine clearance (r = 0.77; p < 0.0001) and for the linear correlation of 1/cystatin C with creatinine clearance (r = 0.73; p < 0.0001). However, we found a significant advantage of cystatin C in detecting a clinical relevant reduction of kidney function (GFR <70 ml/min; p = 0.0047, McNemar test).
  
  
  CONCLUSIONS
  Cystatin C is an alternative marker for the assessment of GFR in renal allograft recipients that may be superior to creatinine.
authors.affiliation: Department of Internal Medicine I, University of Bonn, Germany. u.poege@uni-bonn.de
authors.forename: U
authors.initials: U
authors.lastname: Pöge
authors.forename: B
authors.initials: B
authors.lastname: Stoschus
authors.forename: B
authors.initials: B
authors.lastname: Stoffel-Wagner
authors.forename: T
authors.initials: T
authors.lastname: Gerhardt
authors.forename: H U
authors.initials: HU
authors.lastname: Klehr
authors.forename: T
authors.initials: T
authors.lastname: Sauerbruch
authors.forename: R P
authors.initials: RP
authors.lastname: Woitas
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers; D003404:Creatinine / Q000097:blood; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000502:physiology*; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D014184:Transplantation, Homologous
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D003404:Creatinine