title: Serum cystatin C as an endogenous parameter of the renal function in patients with normal to moderately impaired kidney function.
abstract: BACKGROUND
  Cystatin C is a proteinase inhibitor with a low molecular weight. The serum levels of cystatin C are mainly dependent on glomerular filtration rate (GFR) making cystatin C an endogenous parameter of GFR. The aim of the study was to elucidate the applicability of serum cystatin C as a parameter of GFR in patients with normal to moderately impaired kidney function and to estimate a reference interval for serum cystatin C.
  
  
  METHODS
  Forty-six patients (25 males and 21 females) aged 22 to 83 years with various kidney diseases and 250 blood donors (164 males and 86 females) aged 19 to 64 years were included. Cystatin C was measured by an automated particle-enhanced nephelometric immunoassay, serum creatinine by an enzymatic and by Jaffé method, urine creatinine by an enzymatic method, and GFR by 99mTc-DTPA clearance.
  
  
  RESULTS
  Serum levels ofcystatin C and creatinine showed increments with decreasing values of 99mTc-DTPA clearance and a linear relationship was found between 99mTc-DTPA clearance and l/serum cystatin C, l/serum creatinine (enzymatic method), and creatinine clearance. Comparison of the non-parametric receiver-operating characteristic (ROC) plots for serum cystatin C (area under the curve (AUC) = 0.996; SE = 0.005), serum creatinine (enzymatic method) (AUC = 0.899; SE = 0.044), serum creatinine (Jaffé method) (AUC = 0.870; SE = 0.051), measured creatinine clearance (AUC = 0.959; SE = 0.025), and estimated creatinine clearance (0.950; SE = 0.029) revealed significant differences for serum cystatin C and serum creatinine (enzymatic and Jaffé method) (p values: 0.03 and 0.01). No significant differences were demonstrated between serum cystatin C and measured and estimated creatinine clearance (p value: 0.14 and 0.12). The non-parametric reference interval for serum cystatin C was calculated to be 0.51-1.02 mg/l (median: 0.79 mg/l; range: 0.33 - 1.07 mg/l).
  
  
  CONCLUSIONS
  Serum cystatin C seems to be a better parameter of GFR than serum creatinine in adults with various types of kidney disease with normal to moderately impaired kidney function.
authors.affiliation: Department of Internal Medicine, Viborg Hospital, Denmark.
authors.forename: E
authors.initials: E
authors.lastname: Randers
authors.forename: E J
authors.initials: EJ
authors.lastname: Erlandsen
authors.forename: O L
authors.initials: OL
authors.lastname: Pedersen
authors.forename: C
authors.initials: C
authors.lastname: Hasling
authors.forename: H
authors.initials: H
authors.lastname: Danielsen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D015853:Cysteine Proteinase Inhibitors / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000502:physiology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged
chemical_list: C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors