A-336 A Comparison of eGFR Equation Performance at a Tertiary Care Pediatric Hospital: Evaluating CKD Staging in Young Adults with Impaired Renal Function

Background Young adults with chronic kidney disease (CKD) likely encounter a challenge due to lack of continuity between pediatric to adult eGFR equations. Pierce et al. derived a new set of equations (CKiD U25) to improve glomerular filtration rate (eGFR) estimation in pediatric populations, in 2021. The CKiD U25 consists of three calculations: an eGFR using serum creatinine (CKiD U25(Cr)), cystatin C (CKiD U25(CysC)), and a combined mean (CKiD U25(Cr-CysC)). The objectives of this analysis were (1) to determine variations in CKD staging between CKiD U25(Cr) and CKiD U25(Cr-cysC) equations and (2) compare CKD staging classifications in young adults (17-26 yrs) using the adult CKD-EPI 2021(Cr-CysC) equation and the CKiD U25(Cr-CysC). Methods A retrospective data analysis was performed on all eGFR results (N=8,723, Age:1–26 yrs) reported using the CKiD U25(Cr-CysC) equation between 01/01/2023 and 01/31/2025. CKD stages were assigned to eGFR values derived from the CKiD U25(Cr) and CKiD U25(Cr-CysC) equations based on CKD staging guidelines. Then, we examined variations in CKD staging across all age groups by assessing the proportion of discordant classifications based on the CKiD U25(Cr) and (Cr-CysC) eGFR equations. Next, eGFR results from individuals aged 17–26 years (N=2149) were extracted from the cohort. These results were further stratified into two groups based on the severity of kidney impairment:<30 mL/min/1.73 m²(N=47) and 30–60 mL/min/1.73 m²(N=206). Additionally, eGFR was calculated using the CKD-EPI 2021(Cr-CysC) combined equation for this age group, and regression analysis was performed to compare these values with CKiD U25(Cr-CysC)-derived eGFR. Finally, we assessed variations in CKD staging based on the two equations. Results In our cohort (all age groups, n=8,723, eGFR), both the CKiD U25(Cr-CysC) and CKiD U25(Cr) equations classified patients in the same CKD stage in 6,894 instances (79%). Of the remaining cases, 1,500 (17%) were under-staged to a less severe category, while 329 (4%) were over-staged to a more severe category by the CKiD U25(Cr) equation. Notably, in the young adult subgroup (17-26 yrs) with severely impaired kidney (<30 mL/min/1.73 m²), 13% of cases over staged CKD using the CKiD U25(Cr) equation with no instances of understaging compared to the CKiD U25(Cr-CysC). Additionally, when comparing to the CKD-EPI 2021(Cr-CysC) equation for this subgroup with severely impaired kidney, there was 81% agreement in CKD staging, while 19% were over-staged using the CKD-EPI 2021(Cr-CysC) equation compared to the CKiD U25(Cr-CysC) equation. Regarding kidney transplant candidacy (eGFR<20 mL/min/1.73 m²), 16 patients were classified as candidates under both equations, additional 12 patients met the transplant candidacy criteria only when using the CKD-EPI 2021(Cr-CysC) equation. Conclusion Overall, our health system*s population demonstrates similar CKD staging for the majority of eGFR values estimated using the CKiD U25(Cr-cysC) and CKiD U25(Cr) equations. While the CKD-EPI 2021(Cr-CysC) equation tended to under-stage patients with normal and mildly impaired kidney function, our findings indicate that, it overstated CKD severity compared to CKiD U25(Cr-cysC) equation in patients with severely impaired kidneys. Further investigation is needed to determine whether observed discordant staging results arose from clinical factors affecting cystatin C/Creatinine, or solely from equation differences.