Diagnostic Accuracy of Cystatin C–Based eGFR Equations at Different GFR Levels in Children

Abstract

Summary

Background and objectives The diagnostic accuracy of cystatin C estimated GFR (eGFR) by various cystatin C equations have varied in different studies. We hypothesized that the GFR level of enrolled patients affects the diagnostic accuracy of a cystatin C equation.

Design, setting, participants, & measurements We analyzed 240 consecutively enrolled children at a single Canadian center in a prospective and cross-sectional study. Cystatin C was analyzed with nephelometry, and cystatin C eGFR was estimated by the equations validated in children. GFR was measured by technetium-99m–diethylene-triamine penta-acetic acid (^99mTc DTPA).

Results We compared various cystatin C equations across GFR strata <60, <90, ≥135, and ≥150 ml/min per 1.73 m² for an accurate prediction and appropriate classification of the measured GFR. The CKiD, Zappitelli-CysEq, and Zappitelli-CysCrEq equations had a higher accuracy, estimated by eGFR values within 10% and 30% of the respective ^99mTc DTPA, in the GFR categories <60 and <90 ml/min per 1.73 m², whereas the Bökenkamp, Bouvet, and Filler equations had a greater accuracy in the GFR categories ≥135 and ≥150 ml/min per 1.73 m². The Bouvet, CKiD, Filler, Zappitelli-CysEq, and Zappitelli-CysCrEq equations had a greater sensitivity to classify GFR <60 and <90 ml/min per 1.73 m², whereas the Bökenkamp equation had a higher sensitivity for GFR ≥135 and ≥150 ml/min per 1.73 m².

Conclusions The diagnostic accuracy of various cystatin C equations varies with GFR. This issue needs consideration while applying these equations in clinical practice and for further research on eGFR equations.