Diagnostic Accuracy of Cystatin C–Based eGFR Equations at Different GFR Levels in Children
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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 (⁹⁹m)Tc 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 (99m)Tc 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.
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