title: Clinical usefulness of serum cystatin C and the pertinent estimation of glomerular filtration rate based on cystatin C.
abstract: OBJECTIVE
  Although cystatin C has been developed as an alternative marker for estimating glomerular filtration rate (GFR), its clinical use is as yet limited. The significance of cystatin C for differentiating chronic kidney disease (CKD) stages and established cystatin C-based equations estimating GFR were evaluated.
  
  
  METHODS
  The fresh frozen serum samples from CKD (n = 119) and healthy volunteers (n = 22) were evaluated. Serum creatinine (sCr) was measured by the kinetic Jaffé method, and recalibrated to the isotope dilution mass spectrometry (IDMS). Cystatin C was measured using a particle-enhanced nephelometric assay.
  
  
  RESULTS
  CKD stages were more sensitively differentiated by cystatin C compared to sCr, especially in moderate and severe kidney dysfunction. Sex and body mass index did not affect cystatin C level. Pearson's correlation coefficients of reciprocal of cystatin C, measured and recalibrated sCr compared to systemic inulin clearance (Cl(in) ) were 0.757, 0.734 and 0.709, respectively. We derived novel pertinent equations based on cystatin C (model 1: 1.404 × cystatin C(-0.895)  × age(0.006) × weight(1.074) × height(-1.562)  × (0.865; if female); model 2: 43.287 × cystatin C(-0.906) × age(0.101) × (0.762; if female)]. Models 1 and 2 showed superior performance in representing systemic Cl(in) than the IDMS Modification of Diet in Renal Disease (MDRD) study equations did (adjusted r(2) = 0.76 and 0.72 for models 1 and 2, and 0.64 and 0.65 for 4 and 6 variable IDMS MDRD equations, respectively).
  
  
  CONCLUSIONS
  Cystatin C reflects kidney dysfunction sensitively, and thus cystatin C-based estimation of GFR could provide a reliable support for clinical practice.
authors.affiliation: Department of Internal Medicine Clinical Pharmacology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Ran-Hui
authors.initials: RH
authors.lastname: Cha
authors.forename: Chung Sik
authors.initials: CS
authors.lastname: Lee
authors.forename: Youn-Hee
authors.initials: YH
authors.lastname: Lim
authors.forename: Ho
authors.initials: H
authors.lastname: Kim
authors.forename: Seung Hwan
authors.initials: SH
authors.lastname: Lee
authors.forename: Kyung Sang
authors.initials: KS
authors.lastname: Yu
authors.forename: Yon Su
authors.initials: YS
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood*; D007723:Korea; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000175:diagnosis*; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D003404:Creatinine