title: Agreement between two routine methods of estimation of glomerular filtration rate in patients with advanced and terminal chronic renal failure.
abstract: BACKGROUND
  Estimations of glomerular filtration rate (GFR) obtained either by the modification of diet in renal disease study equation (MDRD-GFR) or by classic 24-hour urine collection-based methods (mean of creatinine and urea clearance (Ccr-ur)) are considered to be equivalent in patients with chronic renal failure (CRF). However, the agreement between both methods has been insufficiently studied in patients during the most advanced stages of CRF.
  
  
  METHODS
  We compared 615 estimations of GFR performed by both methods simultaneously in adult (> 18 years) patients with advanced (aCRF) (15 - 30 ml/min/1.73m2) and preterminal (tCRF) (< 15 ml/min/1.73m2) chronic renal failure. We also analyzed the influence of some relevant covariables (demographic characteristics, inflammatory and nutritional markers) with respect to the concordance between both methods.
  
  
  RESULTS
  In aCRF, mean GFR were 19.7 +/- 5.5 (MDRD-GFR) and 19.3 +/- 3.7 ml/min/1.73m2 (Ccr-ur) (mean difference 0.4 ml/min/1.73m2, 95% confidence interval CI -0.3/1.1, p = 0.26), with an intraclass correlation coefficient of 0.46. In tCRF, mean GFR was 12.5 +/- 4.2 and 10.4 +/- 2.7 ml/min/1.73m2, respectively (mean difference 2.1 ml/min/1.73m2, 95% CI 1.7/2.4, p < 0.0005), with an intraclass correlation co-efficient of 0.43. Multivariate analysis identified lean body mass, body mass index, protein nitrogen appearance, proteinuria, gender, age, albumin (aCRF) and prealbumin (tCRF) as variables independently correlated with the difference MDRD-GFR minus Ccr-ur. Lean body mass was by far the strongest predictor of deviations between both methods, both in aCRF (R2 = 0.66, p < 0.0005) and tCRF (R2 = 0.49, p < 0.0005).
  
  
  CONCLUSIONS
  MDRD-GFR and Ccr-ur show an acceptable agreement in advanced stages of chronic renal failure. However, MDRD-GFR produces estimations of GFR systematically higher than those given by the Ccr-ur method, in patients with tCRF. Moreover, this overestimation is particularly marked in some high risk subsets, including elderly patients and those presenting markers of a poor nutritional condition. Until this issue is further clarified, GFR should be estimated using Ccr-ur rather than MDRD-GFR in patients with tCRF, as also in older and malnourished patients with aCRF, as this may represent a more conservative and safer approach at the time of planning initiation of renal replacement therapy.
authors.affiliation: Division of Nephrology, Hospital Juan Canalejo, A Corunia, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Garcia-Naveiro
authors.forename: A
authors.initials: A
authors.lastname: Rodriguez-Carmona
authors.forename: M
authors.initials: M
authors.lastname: Pérez-Fontán
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D016001:Confidence Intervals; D003404:Creatinine / Q000097:blood / Q000652:urine; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood / Q000503:physiopathology* / Q000652:urine; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D012189:Retrospective Studies; D012720:Severity of Illness Index; D014508:Urea / Q000097:blood / Q000652:urine
chemical_list: D014508:Urea; D003404:Creatinine