John S Fleming1. 1. Department of Medical Physics and Bioengineering, Southampton University Hospitals NHS Trust, UK. john.fleming@suht.swest.nhs.uk
Abstract
OBJECTIVES: Glomerular filtration rate (GFR) is commonly assessed by plasma sampling using the slope-intercept technique. This method assumes a single exponential approximation to the plasma curve. To obtain an accurate estimate of GFR it is necessary to correct the slope-intercept value for the approximation. This is commonly done using the Brochner-Mortensen equation. This has been validated for normal and abnormally low GFRs, but there has been some suggestion that it may underestimate supra-normal GFR. This paper investigates this suggestion and aims to produce a new equation based on compartmental analysis, which should extrapolate the correction to higher values of GFR. METHODS: Compartmental analysis was used to produce the complete expression of the relationship between true GFR and slope-intercept GFR. A simplified analytical equation was then derived. The performance of the new equation was compared to the Brochner-Mortensen and Chantler equations using the true GFR as reference. RESULTS: The new analytical equation had minimal systematic error compared to true GFR up to 250 ml x min(-1) per 1.73 m(2). The Brochner-Mortensen equation was shown to underestimate high values of GFR. The error increased with GFR with a 10% underestimation at 180 ml x min(-1) per 1.73 m(2). The Chantler equation gave a systematic overestimate of GFR. The error increased with GFR with a 30% overestimate at 180 ml x min(-1) per 1.73 m(2). CONCLUSIONS: The new equation described in this paper gave considerably improved correction for the single exponential approximation at high GFR compared to previously described equations.
OBJECTIVES: Glomerular filtration rate (GFR) is commonly assessed by plasma sampling using the slope-intercept technique. This method assumes a single exponential approximation to the plasma curve. To obtain an accurate estimate of GFR it is necessary to correct the slope-intercept value for the approximation. This is commonly done using the Brochner-Mortensen equation. This has been validated for normal and abnormally low GFRs, but there has been some suggestion that it may underestimate supra-normal GFR. This paper investigates this suggestion and aims to produce a new equation based on compartmental analysis, which should extrapolate the correction to higher values of GFR. METHODS: Compartmental analysis was used to produce the complete expression of the relationship between true GFR and slope-intercept GFR. A simplified analytical equation was then derived. The performance of the new equation was compared to the Brochner-Mortensen and Chantler equations using the true GFR as reference. RESULTS: The new analytical equation had minimal systematic error compared to true GFR up to 250 ml x min(-1) per 1.73 m(2). The Brochner-Mortensen equation was shown to underestimate high values of GFR. The error increased with GFR with a 10% underestimation at 180 ml x min(-1) per 1.73 m(2). The Chantler equation gave a systematic overestimate of GFR. The error increased with GFR with a 30% overestimate at 180 ml x min(-1) per 1.73 m(2). CONCLUSIONS: The new equation described in this paper gave considerably improved correction for the single exponential approximation at high GFR compared to previously described equations.
Authors: Derek K S Ng; George J Schwartz; Lisa P Jacobson; Frank J Palella; Joseph B Margolick; Bradley A Warady; Susan L Furth; Alvaro Muñoz Journal: Kidney Int Date: 2011-06-08 Impact factor: 10.612
Authors: Pierre Delanaye; Emmanuelle Vidal-Petiot; Thomas Stehlé; Laurence Dubourg; François Gaillard; Gunnar Sterner; Christine A White; Sandrine Lemoine; Vincent Audard; Dominique Prié; Etienne Cavalier; Marie Courbebaisse; Hans Pottel; Martin Flamant Journal: Kidney Int Rep Date: 2021-03-31