title: Development of a modified sampling and calculation method for isotope plasma clearance assessment of the glomerular filtration rate in patients with cirrhosis and ascites.
abstract: OBJECTIVE
  The aim of this study was to identify a practical sampling regimen and calculation method that could be used to measure the glomerular filtration rate in patients with ascites using plasma sampling.
  
  
  METHODS
  Thirteen potential liver transplant patients with cirrhosis and ascites were injected with Cr-51 ethylenediaminetetraacetic acid, and plasma samples were obtained at up to 16 time points for each patient. Reference clearance values were calculated using the area under the plasma clearance curve, which was calculated using all the available data points. Clearance calculations were then performed using three and four data points from each patient and three different calculation methods to identify a sampling regimen and calculation method that yielded good agreement with the reference values.
  
  
  RESULTS
  The reference clearances ranged from 6 to 80 ml/min. Sampling at 2, 4, 8 and 24 h and calculation of the area under the plasma clearance curve using a log-linear trapezoidal rule with extrapolation to zero and infinity yielded a relative root mean square difference from the reference of less than 7%.
  
  
  CONCLUSIONS
  This method for measuring glomerular filtration rate in patients with cirrhosis and ascites was found to be more accurate than the slope-intercept technique and is a practical alternative to urine collection.
authors.affiliation: aNuclear Medicine Department bThe Sheila Sherlock Liver Centre, Royal Free London NHS Foundation Trust cUCL Institute of Liver and Digestive Health, University College London, London, UK dMedical Imaging Department, University of Saskatchewan, Saskatoon, Saskatchewan eFaculty of Medicine, Memorial University of Newfoundland, St Johns, Newfoundland, Canada.
authors.forename: Fred
authors.initials: F
authors.lastname: Wickham
authors.forename: Maria T
authors.initials: MT
authors.lastname: Burniston
authors.forename: Elias
authors.initials: E
authors.lastname: Xirouchakis
authors.forename: Eleni
authors.initials: E
authors.lastname: Theocharidou
authors.forename: Carl A
authors.initials: CA
authors.lastname: Wesolowski
authors.forename: Andrew J W
authors.initials: AJ
authors.lastname: Hilson
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Burroughs
mesh_terms: D000465:Algorithms; D019540:Area Under Curve; D001201:Ascites / Q000097:blood / Q000378:metabolism*; D001774:Blood Chemical Analysis / Q000379:methods*; D002860:Chromium Radioisotopes / Q000493:pharmacokinetics; D004492:Edetic Acid / Q000493:pharmacokinetics*; D005919:Glomerular Filtration Rate; D006801:Humans; D008103:Liver Cirrhosis / Q000097:blood / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D013997:Time Factors
chemical_list: D002860:Chromium Radioisotopes; D004492:Edetic Acid