title: Comparison of glomerular filtration rates calculated by different serum cystatin C-based equations in patients with chronic kidney disease.
abstract: BACKGROUND
  We aimed to evaluate the performance of serum cystatin C-based equations in calculating the glomerular filtration rate (GFR) in patients with varying stages of chronic kidney disease (CKD).
  
  
  METHODS
  Serum cystatin C and creatinine levels were measured in 615 CKD patients. The CKD stage was determined by the creatinine-based estimated GFR (eGFR) equation using the four-variable abbreviated Modification of Diet in Renal Disease equation suggested by the Kidney Disease Outcome Quality Initiative with the addition of a coefficient applicable to Korean populations (K-aMDRD). In each CKD stage, the ratio of serum cystatin C to creatinine was calculated and six different cystatin C-based equations were used to estimate GFR. Cystatin C-based eGFR and aMDRD eGFR values were compared using the paired t test, Pearson correlation test, and the Bland-Altman plot.
  
  
  RESULTS
  The mean age of patients was 53.21±14.45 years; of the 615 patients, 346 were male. The serum cystatin C-to-creatinine ratio was inversely correlated with the CKD stage. Compared with the K-aMDRD values, the results of the Hoek, Filler, and Le Bricon's cystatin C-based eGFR equations were lower in CKD Stages 1-3 and higher in Stages 4 and 5. However, the results of the Orebro-cystatin (Gentian) equation [GFR=100/ScytC (mL/minute/1.73 m(2)) - 14] were similar to those of the K-aMDRD equation in CKD Stages 4 and 5 (15.44±9.45 vs. 15.17±9.05 mL/minute/1.73 m(2), respectively; P=0.722; bias=0.27±8.87).
  
  
  CONCLUSIONS
  The eGFRs obtained from the six cystatin C-based equations differed widely. Therefore, further studies are required to determine the most accurate equation to estimate GFR in Koreans with CKD.
authors.affiliation: Department of Internal Medicine, Youngdo Hospital, Busan, Korea.
authors.forename: Hee Sun
authors.initials: HS
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea; Biomedical Research Institute, Pusan National University Hospital, Busan, Korea.
authors.forename: Harin
authors.initials: H
authors.lastname: Rhee
authors.affiliation: Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea; Biomedical Research Institute, Pusan National University Hospital, Busan, Korea.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Seong
authors.affiliation: Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea.
authors.forename: Dong Won
authors.initials: DW
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea.
authors.forename: Soo Bong
authors.initials: SB
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea; Biomedical Research Institute, Pusan National University Hospital, Busan, Korea.
authors.forename: Ihm Soo
authors.initials: IS
authors.lastname: Kwak
keywords: Chronic kidney disease; Cystatin C; Estimated glomerular filtration rate; Serum creatinine