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

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 m(2) 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 m(2), whereas the Bokenkamp, Bouvet, and Filler equations had a greater accuracy in the GFR categories >= 135 and >= 150 ml/min per 1.73 m(2). 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 m(2), whereas the Bokenkamp equation had a higher sensitivity for GFR >= 135 and >= 150 ml/min per 1.73 m(2). 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. Clin J Am Soc Nephrol 6: 1599-1608, 2011. doi: 10.2215/CJN.10161110