title: Evaluation of single sample clearance calculations in 902 patients. A comparison of multiple and single sample techniques.
abstract: OBJECTIVE
  To derive new formulae for the calculation of single sample clearance of the contrast medium iohexol and to compare the formulae to a selection of existing single sample clearance formulae derived for the calculation of 51Cr-EDTA and 99mTc-DTPA clearance.
  
  
  METHODS
  Glomerular filtration rate (GFR) was calculated from total plasma clearance of iohexol used for urography in 902 patients. Two plasma samples were drawn in each patient. Automated x-ray fluorescence analysis equipment was used for the plasma iodine analysis. Single and multiple sample iohexol clearance values were compared. In 77 patients the multiple sample clearance values were additionally compared to a 51Cr-EDTA clearance performed simultaneously or within 14 days.
  
  
  RESULTS
  The precision of the results calculated by the existing single sample clearance formulae and the derived iohexol single sample clearance formulae were essentially the same. The most precise of the derived formulae was that based on the Bak Christensen & Groth formula. The correlation between multiple sample clearance of iohexol and 51Cr-EDTA was high (r = 0.918).
  
  
  CONCLUSIONS
  Iohexol can substitute 51Cr-EDTA for GFR measurement. A valid GFR can be calculated from a single plasma sample determination of iohexol clearance using either the existing formulae or the new formulae derived from the present study.
authors.affiliation: Department of Diagnostic Radiology, University Hospital, Umeå, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Lundqvist
authors.forename: S O
authors.initials: SO
authors.lastname: Hietala
authors.forename: S
authors.initials: S
authors.lastname: Groth
authors.forename: J G
authors.initials: JG
authors.lastname: Sjödin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002860:Chromium Radioisotopes / Q000008:administration & dosage / Q000493:pharmacokinetics*; D003287:Contrast Media / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004492:Edetic Acid / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007275:Injections, Intravenous; D007472:Iohexol / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D012588:Scintillation Counting / Q000706:statistics & numerical data; D013052:Spectrometry, X-Ray Emission / Q000706:statistics & numerical data; D013997:Time Factors; D014567:Urography
chemical_list: D002860:Chromium Radioisotopes; D003287:Contrast Media; D007472:Iohexol; D004492:Edetic Acid