Background: Numerous equations have been reported for the estimation of glomerular filtration rate (eGFR) based on serum creatinine. Serum cystatin C-based equation has been recently demonstrated to be better in estimating GFR. This study was conducted to examine the agreement between eGFR measured by equations based on serum creatinine (eGFRCr) and cystatin C (eGFRCys) or both (eGFRCrCys) in children with chronic kidney disease (CKD).
Methods: This prospective observational study was conducted in children less than 14-years with CKD stage 2-4. CKiD equation was used for calculation of eGFRCr and eGFRCys. Considering the eGFRCr as reference standard, we assessed the agreement of eGFRCr with eGFRCys and eGFRCrCys estimated by constructing a Bland-Altman plot and visually estimating the distribution of points representing the difference between eGFRCr and eGFRCys or eGFRCrCys against the line of zero difference.
Results: A total of 60 patients (54 boys) with mean age of 88±47 months were enrolled. Overall, 57%, 35% & 8% children had CKD stage 2, 3, and 4 respectively. The mean eGFRCr, eGFRCys and eGFRCrCys was 58 (19), 55 (21) and 62 (12) ml/min/1.73 m2, respectively. Bias between eGFRCr and eGFRCys was 2.8 (95% CI: -1.03 to 6.6) ml/min/1.73 m2. Bias between eGFRCr and eGFRCrCys was -4.5(95% CI: -6.5 to -2.5) ml/min/1.73 m2.
Conclusion: Serum creatinine-based equation slightly overestimates the GFR when compared with eGFRCrCys with overall average agreement between equations in children with pre-dialysis CKD. For GFR estimation, the combination of serum creatinine and serum cystatin C is more precise than either marker alone.