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Correct evaluation of renal glomerular filtration rate requires clearance assays
Lars Hjorth1, Thomas Wiebe, Diana Karpman
1Division of Oncology-Hematology, Department of Pediatrics, University Hospital, 221 85 Lund, Sweden. Lars.Hjorth@pedi.lu.se
Insights
Iohexol clearance is the gold standard for measuring glomerular filtration rate (GFR) in children. Simpler methods like serum creatinine and cystatin C, and various formulas, do not accurately predict GFR and cannot replace iohexol clearance.
Area of Science:
- Nephrology
- Pediatrics
- Clinical Chemistry
Background:
- Iohexol clearance is an established but lengthy method for determining glomerular filtration rate (GFR).
- Accurate GFR measurement is crucial, especially in pediatric patients with hematological-oncological disorders.
- Simpler, faster alternatives for GFR assessment are sought to improve clinical workflow.
Purpose of the Study:
- To evaluate the predictive accuracy of simpler methods for estimating GFR in children.
- To determine if serum creatinine, serum cystatin C, or established GFR formulas can replace iohexol clearance.
- To assess the reliability of alternative GFR estimation methods in a pediatric oncology population.
Main Methods:
- Regression analysis was used to establish linear relationships between iohexol clearance and five alternative parameters: 1/serum creatinine, serum cystatin C, and the Schwartz, Counahan-Barratt, and modified Counahan-Barratt formulas.
- The standard deviation of residuals (S(res)) was calculated to quantify the variation in GFR prediction for each method.
- Analyses were performed comparing multiple measurements per individual and single measurements per individual.
Main Results:
- Linear correlations were observed between iohexol clearance and all tested parameters (r values ranging from 0.41 to 0.48).
- The standard deviation of residuals (S(res)) indicated significant variation in GFR prediction, with values ranging from 38 to 43 ml/min per 1.73 m(2).
- These variations were not substantially reduced when comparing single GFR measurements per child, indicating poor predictive accuracy.
Conclusions:
- Despite observed correlations, simpler methods for GFR estimation, including serum creatinine, serum cystatin C, and the evaluated formulas, exhibit substantial variability.
- These alternative methods cannot reliably replace iohexol clearance for accurate GFR measurement in the studied pediatric population.
- Further research may be needed to develop more precise and efficient GFR assessment tools for children.
Abstract:
Iohexol clearance is an accepted, but time-consuming assay for the measurement of glomerular filtration rate (GFR). We investigated if simpler methods could predict GFR. Sixty-nine children with hematological-oncological disorders participated. A linear relationship was established by regression analysis between iohexol clearance ( n=734) and 1/s-creatinine ( r=0.45, n=727), s-cystatin C ( r=0.41, n=518), and the Schwartz ( r=0.45, n=723), Counahan-Barratt ( r=0.48, n=723), and modified Counahan-Barratt formulae ( r=0.48, n=723). These correlations improved when one GFR measurement per individual was compared with each of the five parameters. We further investigated if iohexol clearance could accurately be replaced. The degree of variation in predicting GFR was estimated by the standard deviation of the residuals (S(res)). For 1/s-creatinine and s-cystatin C, S(res) was 39 and 38 ml/min per 1.73 m(2). For the formulae of Schwartz, Counahan-Barratt, and modified Counahan-Barratt, the S(res) was 43, 40, and 40 ml/min per 1.73 m(2), respectively. The wide variations of the S(res) were not reduced when one GFR measurement per child was compared with the five parameters. Due to the large deviation in predicting GFR, we conclude that the five alternative methods studied cannot replace iohexol clearance for measurement of GFR.