title: Measurement of the kidney function in patients with rheumatoid arthritis: plasma cystatin C versus 51Cr-EDTA clearance.
abstract: OBJECTIVE
  Knowledge of the usefulness of cystatin C measurement in the detection of chronic kidney disease in patients with rheumatoid arthritis (RA) is scant. The purpose of this study was to evaluate the ability of plasma cystatin C- and creatinine-based methods to predict glomerular filtration rate (GFR) and classify chronic kidney disease in RA patients.
  
  
  METHODS
  The study population consisted of 64 RA patients aged 41-86 years. Comparisons were made between measured plasma creatinine, cystatin C, creatinine clearance and GFR estimated by the Cockcroft-Gault (CG) and the Modification of Diet in Renal Disease (MDRD) formulas. The plasma clearance of (51)Cr-EDTA served as a reference.
  
  
  RESULTS
  The Pearson correlation coefficients between plasma clearance of (51)Cr-EDTA and the markers of GFR were calculated. The correlation coefficients were 0.800 for plasma creatinine, 0.863 for cystatin C, 0.866 and 0.904 for GFR values estimated by MDRD and CG and 0.922 for plasma creatinine clearance. Statistically significant differences were detected between the correlation coefficients of plasma creatinine and GFR estimated by CG (p = 0.0412) and plasma creatinine and creatinine clearance (p = 0.0099). Creatinine clearance and the MDRD and CG formulas proved to be better at identifying GFR <90 ml/min than plasma creatinine or cystatin C.
  
  
  CONCLUSIONS
  We recommend using the CG formula or creatinine clearance for the estimation of the GFR of RA patients instead of solely creatinine or cystatin C in clinical work.
authors.affiliation: Department of Internal Medicine, Tampere University Hospital, Tampere, Finland. krista.karstila@fimnet.fi
authors.forename: Krista
authors.initials: K
authors.lastname: Karstila
authors.forename: Aimo P T
authors.initials: AP
authors.lastname: Harmoinen
authors.forename: Terho J
authors.initials: TJ
authors.lastname: Lehtimäki
authors.forename: Markku M
authors.initials: MM
authors.lastname: Korpela
authors.forename: Jukka T
authors.initials: JT
authors.lastname: Mustonen
authors.forename: Heikki H T
authors.initials: HH
authors.lastname: Saha
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000150:complications*; D002860:Chromium Radioisotopes / Q000493:pharmacokinetics; D003404:Creatinine / Q000097:blood / Q000652:urine; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D004492:Edetic Acid / Q000493:pharmacokinetics; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007118:Immunoassay; D007674:Kidney Diseases / Q000175:diagnosis* / Q000209:etiology / Q000378:metabolism; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry; D012680:Sensitivity and Specificity
chemical_list: C525030:CST3 protein, human; D002860:Chromium Radioisotopes; D055316:Cystatin C; D015891:Cystatins; D004492:Edetic Acid; D003404:Creatinine