title: Reliability of endogenous markers for estimation of residual renal function in haemodialysis patients.
abstract: BACKGROUND
  Residual renal function in haemodialysis patients is of increasing interest. However, reproducibility and agreement between methods to measure and estimate glomerular filtration rate (GFR) require further elucidation. The aim of this study was to evaluate the accuracy and reproducibility of GFR estimates based on endogenous markers in haemodialysis patients.
  
  
  METHODS
  Twelve patients were examined twice. GFR was estimated by (i) urine clearances of creatinine, urea and the average of creatinine and urea clearance [U-Cl(crea-urea)]; (ii) an equation based on serum concentration of cystatin C [eGFR(CysC)]. These were compared to (51) Cr-EDTA clearance in plasma [P-Cl(EDTA)] and urine [U-Cl(EDTA)].
  
  
  RESULTS
  U-Cl(crea-urea) produced results similar to U-Cl(EDTA). eGFR(CysC) had a low week-to-week variability. Visually, eGFR(CysC) differed from y = x when compared to the other methods indicating bias, probably due to extrarenal elimination of cystatin C. Coefficients of variation were significantly different, P<0·001: P-Cl(EDTA), 10%; U-Cl(EDTA), 13%; and U-Cl(crea-urea), 13%. P-Cl(EDTA) was 2·1 ml min(-1) 1·73 m(-2) higher than U-Cl(EDTA) (mean).
  
  
  CONCLUSIONS
  Glomerular filtration rate in haemodialysis patients can be estimated from U-Cl(crea-urea) when complete urine collection is performed. The available eGFR(CysC) in haemodialysis patients seemed to be biased, and further development and validation is desirable. P-Cl(EDTA) was the most reproducible method and might be useful in special situations.
authors.affiliation: Department of Renal Medicine, Aarhus University Hospital, Aarhus, Denmark. krista@ki.au.dk
authors.forename: Krista D
authors.initials: KD
authors.lastname: Kjaergaard
authors.forename: Michael
authors.initials: M
authors.lastname: Rehling
authors.forename: Jens D
authors.initials: JD
authors.lastname: Jensen
authors.forename: Bente
authors.initials: B
authors.lastname: Jespersen
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood / Q000652:urine; D003404:Creatinine / Q000652:urine*; D055316:Cystatin C / Q000097:blood*; D003718:Denmark; D004492:Edetic Acid; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000378:metabolism / Q000503:physiopathology*; D007674:Kidney Diseases / Q000097:blood / Q000503:physiopathology / Q000628:therapy* / Q000652:urine; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015999:Multivariate Analysis; D011237:Predictive Value of Tests; D006435:Renal Dialysis; D015203:Reproducibility of Results; D013997:Time Factors; D014508:Urea / Q000652:urine*
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D014508:Urea; D004492:Edetic Acid; D003404:Creatinine