title: Estimation of glomerular filtration rate via 2- and 4-sample plasma clearance of iohexol and creatinine in clinically normal cats.
abstract: OBJECTIVE
  To compare 2 methods for estimation of glomerular filtration rate (GFR), study the effects of age and body size on GFR estimates, and provide a reference range for estimated GFR in clinically normal cats.
  
  
  METHODS
  57 cats.
  
  
  METHODS
  In each cat, GFR was estimated via plasma clearance of iohexol and creatinine. Results of a 1-compartmental model (CL1comp) were calibrated to a trapezoidal method estimate (CLtrap) by use of a correction formula applicable to dogs or humans and standardized to body weight; for iohexol clearance, data were also standardized to extracellular fluid volume (ECFV). For all 57 cats, method comparison was performed via agreement analysis. Reference ranges for GFR derived by the different methods were established by use of data from a subset of 51 cats after exclusion of 6 cats that were azotemic, Birman, or both.
  
  
  RESULTS
  In 57 cats, mean CLtrap of creatinine was 0.29 mL/min/kg (13%) higher than CLtrap of iohexol. In 51 nonazotemic cats, mean CLtrap was 2.26 mL/min/kg for iohexol (reference range, 1.02 to 3.50 mL/min/kg) and 2.55 mL/min/kg for creatinine (reference range, 1.27 to 3.83 mL/min/kg). Values of GFR/kg or GFR standardized to liters of ECFV did not decrease with increasing age. A negative linear relationship was detected between body weight and estimated GFR/kg or GFR standardized to liters of ECFV.
  
  
  CONCLUSIONS
  Reference ranges for estimated GFR via plasma clearance of iohexol and creatinine should facilitate early detection of impaired renal function in cats, although body weight should be taken into account.
authors.affiliation: Department of Companion Animal Clinical Sciences, Norwegian School of Veterinary Science, 0033 Oslo, Norway.
authors.forename: Reidun
authors.initials: R
authors.lastname: Heiene
authors.forename: Brice S
authors.initials: BS
authors.lastname: Reynolds
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: Bexfield
authors.forename: Stig
authors.initials: S
authors.lastname: Larsen
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Gerritsen
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight; D002415:Cats; D003404:Creatinine / Q000097:blood / Q000493:pharmacokinetics*; D005919:Glomerular Filtration Rate / Q000662:veterinary*; D007472:Iohexol / Q000493:pharmacokinetics*; D007677:Kidney Function Tests / Q000379:methods / Q000662:veterinary*; D008657:Metabolic Clearance Rate
chemical_list: D007472:Iohexol; D003404:Creatinine