title: Significant differences when using MDRD for GFR estimation compared to radionuclide measured clearance.
abstract: OBJECTIVE
  To evaluate Estimated Glomerular Filtration Rate (eGFR), using the Modification of Diet in Renal Disease equation, and compare with radionuclide GFR (rGFR) in a Radiology setting to assess renal function prior to contrast administration.
  
  
  METHODS
  Five hundred and sixteen retrospective rGFR studies from a mixed referral population were selected and the eGFR calculated. Regression and Bland-Altman analysis was performed. The percentage of rGFR and eGFR studies below 30 ml/min/1.73 m² and 60 ml/min/1.73 m² were calculated; these are important thresholds for classifying renal insufficiency.
  
  
  RESULTS
  A significant correlation between eGFR and rGFR (R² = 0.62, p < 0.0001) and significant differences in the medians (p < 0.0001) were found. eGFR overestimated rGFR with a bias (mean difference) of 10.8 ml/min/1.73 m² over the whole range of rGFR. Studies with an rGFR of under 30 ml/min/1.73 m² had a mean bias of 4.6 ml/min/1.73 m² (difference range -5.9 to 26.3 ml/min/1.73 m²). The bias over the range 30 to 60 ml/min/1.73 m² was 13.2 ml/min/1.73 m² (difference range -16.8 to 88.3 ml/min/1.73 m²). In 25.4% of studies, eGFR was less than 60 ml/min/1.73 m² compared with 40.5% of rGFR studies.
  
  
  CONCLUSIONS
  Awareness of the bias between eGFR and rGFR is important when assessing Radiology patients for risks of nephrotoxicity and Nephrogenic Systemic Fibrosis from contrast medium.
authors: Department of Medical Physics, St. George's Hospital, Knightsbridge Wing, Tooting, London, SW17 0QT, UK. allison.craig@stgeorges.nhs.uk
authors: A J
authors: AJ
authors: Craig
authors: A
authors: A
authors: Britten
authors: S D
authors: SD
authors: Heenan
authors: A G
authors: AG
authors: Irwin
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