title: Serum cystatin C measured by automated immunoassay: a more sensitive marker of changes in GFR than serum creatinine.
abstract: Serum cystatin C has been suggested as a new marker of GFR. For the introduction of this marker into clinical use a rapid and automated method is required. We have developed and validated an assay for serum cystatin C using latex particle-enhanced immunoturbidimetry. Intra- and inter-assay precision were < 3% and < 5% across the assay range. Analytical recovery was 93 +/- 3.8% and no lack of parallelism was demonstrated. Regression analysis of a method comparison with an enzyme-enhanced radial-immunodiffusion method, gave PETIA = 0.074 + 0.93 x SRID, r = 0.98, N = 100. Inter-assay precision profiles showed cystatin C was measured with two-fold better precision than creatinine on the same analyzer. Cystatin C measurement was neither interfered with by icterus nor by hemolysis. 1/cystatin C versus 1/creatinine concentrations gave r = 0.67, N = 469. Comparison of Cr EDTA GFR with 1/cystatin C and 1/creatinine gave r = 0.81 and 0.50, respectively, N = 206. Calculating diagnostic sensitivity for abnormal GFR showed cystatin C to be significantly (P < 0.05) more sensitive than creatinine (71.4 vs. 52.4%). Cystatin C measurement using PETIA technology can be automated on the same instruments used routinely for the measurement of creatinine and offers better analytical performance and probably improved clinical sensitivity as a screening test for early renal damage.
authors.affiliation: Department of Clinical Biochemistry, London Hospital Medical College, England, United Kingdom.
authors.forename: D J
authors.initials: DJ
authors.lastname: Newman
authors.forename: H
authors.initials: H
authors.lastname: Thakkar
authors.forename: R G
authors.initials: RG
authors.lastname: Edwards
authors.forename: M
authors.initials: M
authors.lastname: Wilkie
authors.forename: T
authors.initials: T
authors.lastname: White
authors.forename: A O
authors.initials: AO
authors.lastname: Grubb
authors.forename: C P
authors.initials: CP
authors.lastname: Price
mesh_terms: D015415:Biomarkers; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D015853:Cysteine Proteinase Inhibitors / Q000097:blood*; D005919:Glomerular Filtration Rate; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007674:Kidney Diseases / Q000097:blood*; D007840:Latex; D008863:Microspheres; D009391:Nephelometry and Turbidimetry / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D007840:Latex; D003404:Creatinine