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Comparative Study
. 2014 Jan;9(1):54-63.
doi: 10.2215/CJN.00940113. Epub 2013 Nov 7.

New combined serum creatinine and cystatin C quadratic formula for GFR assessment in children

Hassib Chehade  1 , Francois Cachat, Anne-Sophie Jannot, Blaise-Julien Meyrat, Dolores Mosig, Daniel Bardy, Paloma Parvex, Eric Girardin
Affiliations
Comparative Study

New combined serum creatinine and cystatin C quadratic formula for GFR assessment in children

Hassib Chehade et al. Clin J Am Soc Nephrol. 2014 Jan.

Erratum in

  • Clin J Am Soc Nephrol. 2014 Oct 7;9(10):1822

Abstract

Background and objectives: The estimated GFR (eGFR) is important in clinical practice. To find the best formula for eGFR, this study assessed the best model of correlation between sinistrin clearance (iGFR) and the solely or combined cystatin C (CysC)- and serum creatinine (SCreat)-derived models. It also evaluated the accuracy of the combined Schwartz formula across all GFR levels.

Design, setting, participants, & measurements: Two hundred thirty-eight iGFRs performed between January 2012 and April 2013 for 238 children were analyzed. Regression techniques were used to fit the different equations used for eGFR (i.e., logarithmic, inverse, linear, and quadratic). The performance of each model was evaluated using the Cohen κ correlation coefficient and the percentage reaching 30% accuracy was calculated.

Results: The best model of correlation between iGFRs and CysC is linear; however, it presents a low κ coefficient (0.24) and is far below the Kidney Disease Outcomes Quality Initiative targets to be validated, with only 84% of eGFRs reaching accuracy of 30%. SCreat and iGFRs showed the best correlation in a fitted quadratic model with a κ coefficient of 0.53 and 93% accuracy. Adding CysC significantly (P<0.001) increased the κ coefficient to 0.56 and the quadratic model accuracy to 97%. Therefore, a combined SCreat and CysC quadratic formula was derived and internally validated using the cross-validation technique. This quadratic formula significantly outperformed the combined Schwartz formula, which was biased for an iGFR≥91 ml/min per 1.73 m(2).

Conclusions: This study allowed deriving a new combined SCreat and CysC quadratic formula that could replace the combined Schwartz formula, which is accurate only for children with moderate chronic kidney disease.

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Figures

Figure 1.
Figure 1.
Graphs depicting sinistrin clearances (iGFRs) according to cystatin C (CysC) (A), 1/CysC (B), logarithm of CysC (C), and square of CysC (D), using a locally weighted polynomial regression. The solid line represents a local linear polynomial fit (function lowess, package stats).
Figure 2.
Figure 2.
Q-Q plot for residuals of the combined serum creatinine (SCreat) and cystatin C (CysC) quadratic model.
Figure 3.
Figure 3.
Residuals versus sinistrin clearances (iGFRs) and corresponding segments by circular binary segmentation method using the combined serum creatinine (SCreat) and cystatin C (CysC)–based Schwartz formula. eGFR, estimated GFR.
Figure 4.
Figure 4.
Residuals versus sinistrin clearances (iGFRs) and corresponding segments by circular binary segmentation method using the new combined serum creatinine (SCreat) and cystatin C (CysC)–based quadratic formula. eGFR, estimated GFR.
See this image and copyright information in PMC

References

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