ISSN 2398-2950      

Glomerular filtration rate


Synonym(s): Plasma clearance, iohexol clearance, exogenous creatinine clearance, GFR


  • Determination of the glomerular filtration rate (GFR) is the gold standard to assess kidney function.
  • Plasma clearance techniques are mostly used because urinary clearance techniques have more practical limitations. Plasma clearance methods require repeated blood sampling over a period of several hours after intravenous injection of a clearance marker, mostly creatinine or iohexol.
  • The GFR is calculated by dividing the dose of the clearance marker by the area under the plasma concentration-versus-time curve.
  • Multiple protocols have been described, using different doses of creatinine or iohexol, different number of blood samples, different time points for sample collection and different duration of the clearance procedure. In general, the accuracy of the AUC increases with more blood samples and a longer period of collection.
  • Multi-sampling plasma clearance techniques are cumbersome, time-consuming and potentially stressful or painful in cats. Therefore, limited sampling strategies (LSS) or clearance techniques based on a reduced number of blood samples have been described. LSS are a suitable compromise between practical convenience and clinical accuracy for GFR determination.  
  • The clearance protocol used should take into account patient characteristics (eg size, cooperation) and practical issues (eg time, costs).   


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  • Clearance = GFR (ml/min/kg) = dose/AUC.
  • Different methods can be used to calculate the AUC, such as the one-compartmental or two-compartmental model or the assumption free noncompartmental approach.


  • An injectable creatinine solution is not commercialized and can be prepared using anhydrous creatinine powder. Creatinine assays are readily available in veterinary practices and in commercial laboratories.
  • Iohexol is widely available as radiographic contrast material, but iohexol assays are available only in a limited number of laboratories (eg Royal Veterinary College UK, Michigan State University USA).

Technique (intrinsic) limitations

  • Multisample plasma clearance techniques are labor-intensive and expensive. LSS overcome these limitations, but increase the risk for inaccurate GFR estimation.

Result Data

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Further Reading


Other sources of information

  • Recent references from VetMedResource and PubMed.
  • Paepe D, Lefebvre HP, Concordet D, van Hoek I, Croubels S, Daminet S (2015) Simplified methods for estimating glomerular filtration rate in cats and for detection of cats with low or borderline glomerular filtration rate. J Feline Med Surg 17 (10), 889-900 PubMed.
  • Von Hendy-Willson V E, Pressler B M (2011) An overview of glomerular filtration rate testing in dogs and cats. Vet J 188 (2), 156-165 PubMed.
  • Finch N (2014) Measurement of glomerular filtration rate in cats: methods and advantages over routine markers of renal function. J Feline Med Surg 16 (9), 736-748 PubMed.

Other sources of information

  • Heiene R, Lefebvre H P (2013) Glomerular Filtration Rate in Dogs and Cats. Available from: (Cited 21 December 2016).
  • Braun J P, Lefebvre H P (2008) Kidney Function and Damage. In: Clinical biochemistry of domestic animals. Eds: Kaneko J J H, Harvey J W & Bruss M L. 6th edn. Elsevier, UK. pp 485-528.


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