title: Evaluation of plasma cystatin C as a marker for glomerular filtration rate in patients with type 2 diabetes.
abstract: OBJECTIVE
  To evaluate plasma cystatin C as a marker of the glomerular filtration rate in patients with type 2 diabetes and their age and sex-matched controls.
  
  
  METHODS
  Forty-seven patients with one decade of type 2 diabetes and 51 non-diabetic control subjects were studied. Plasma cystatin C was measured by particle-enhanced turbidimetric immunoassay in a new application for the Hitachi 704 analyzer. For comparison, plasma creatinine and creatinine clearance were measured. The plasma clearance of 51Cr-EDTA by the single injection method was utilized as reference.
  
  
  RESULTS
  In patients with type 2 diabetes the correlation coefficient between plasma cystatin C and the plasma clearance of 51Cr-EDTA was 0.774 (Spearman's coefficient) and that between plasma creatinine and the plasma clearance of 51Cr-EDTA was 0.556 (p = 0.001 for the difference). The correlation between creatinine clearance and the plasma clearance of 51Cr-EDTA was 0.411. In receiver operating characteristic (ROC) curve analysis the diagnostic accuracy of plasma cystatin C was significantly better than that of plasma creatinine (p = 0.047) or creatinine clearance (p = 0.001). The best diagnostic efficiency (98%) for cystatin C was obtained when the cut-off limit was set at 1.32 mg/l. In the control group the correlation coefficients were: between cystatin C and the plasma clearance of 51Cr-EDTA 0.627, between creatinine and the plasma clearance of 51Cr-EDTA 0.466 and between creatinine clearance and the plasma clearance of 51Cr-EDTA 0.416. The area under the ROC plot curve of cystatin C was also greatest in the control group, but the diagnostic accuracy of cystatin C was marginally better than that of either plasma creatinine (p = 0.05) or creatinine clearance (p = 0.08). Among the control subjects various non-renal causes may have interfered with cystatin C concentrations reducing the correlations.
  
  
  CONCLUSIONS
  Cystatin C measurement is a more sensitive and specific test for GFR in patients with type 2 diabetes than plasma creatinine or its clearance, when GFR is normal or only slightly reduced. If an elevated cystatin C concentration is found, non-renal factors have to be excluded. The turbidimetric application described here can easily be applied for most clinical chemistry analyzers and is therefore useful in daily clinical practice.
authors.affiliation: Department of Clinical Chemistry, Tampere University Hospital, Finland.
authors.forename: A P
authors.initials: AP
authors.lastname: Harmoinen
authors.forename: T T
authors.initials: TT
authors.lastname: Kouri
authors.forename: O R
authors.initials: OR
authors.lastname: Wirta
authors.forename: T J
authors.initials: TJ
authors.lastname: Lehtimäki
authors.forename: V
authors.initials: V
authors.lastname: Rantalaiho
authors.forename: V M
authors.initials: VM
authors.lastname: Turjanmaa
authors.forename: A I
authors.initials: AI
authors.lastname: Pasternack
mesh_terms: D000368:Aged; D015415:Biomarkers; D003401:Creatine / Q000097:blood; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000503:physiopathology*; D005069:Evaluation Studies as Topic; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D016555:Matched-Pair Analysis; D008657:Metabolic Clearance Rate
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D003401:Creatine