# Switching to the CKD-EPI but Not Modified FAS eGFR Formula Underdetects CKD Among Adolescents and Young Adults in México

## TL;DR

Switching to the CKD-EPI formula for estimating kidney function in young adults in Mexico leads to fewer cases of chronic kidney disease being detected compared to other formulas.

## Contribution

The study highlights the underdetection of CKD in adolescents and young adults in Mexico when using the CKD-EPI formula instead of other eGFR estimation methods.

## Key findings

- CKD-EPI eGFR values were significantly higher than CKiD-U25 values, leading to fewer CKD cases being identified.
- Modified Schwartz and Pottel FAS formulas showed better correlation with each other than with CKD-EPI.
- CKD-EPI identified only 4.8% of participants as having CKD 2+, compared to 37.7% with CKiD-U25.

## Abstract

Background: Guidelines recommend switching the glomerular filtration rate (eGFR) estimation from the CKiD-U25 to the CKD-EPI formula at age 18. We investigated how this would affect chronic kidney disease (CKD) classification. Methods: Serum creatinine was enzymatically measured in 1061 samples from 914 community-based 10–23-year-olds from Tlaxcala, Mexico, a region where urinary biomarkers demonstrated early kidney damage associated with exposure to inorganic toxins in a pediatric population. We calculated their eGFR using CKiD-U25, modified Schwartz, the first and modified Pottel full-age spectrum (FAS), and CKD-EPI formulae. Correlation analysis characterized the CKD stage stratified by age and sex. Results: At baseline, the median age was 13 (IQR: 12, 15) years, and 55% were female. Median CKiD-U25 eGFR was 96.9 (IQR: 83.3, 113.3) mL/min/1.73 m2, significantly lower than the CKD-EPI eGFR, which was 140.8 (IQR: 129.9, 149.3) mL/min/1.73 m2 (p < 0.0001, Wilcoxon rank test). The mean bias was 36.99 ± 12.89 mL/min/1.73 m2. Pearson correlation was r = 0.8296 (95% confidence interval 0.0898–0.8474). There was a better correlation between the modified Schwartz (r = 0.9421 (0.9349, 0.9485)) and the Pottel FAS (r = 0.9299 (0.9212, 0.9376)) formulae. Agreement was deficient when the eGFR was >75 mL/min/1.73 m2 in younger age and female sex. Modified Schwartz identified 281 (26.4%) measurements as having CKD 2 and 3 (2+), U25 identified 401 (37.7%) measurements as having CKD 2+, FAS identified 267 (25.1%) and modified FAS identified 282 (30%) measurements as having CKD 2+, and CKD-EPI identified 51 (4.8%) measurements as having CKD 2+, respectively. Conclusions: In this population, there needed to be better agreement between the various eGFR formulae. CKD-EPI identifies substantially fewer at-risk participants as having CKD.