Wang et al1 evaluated discordances in the estimated glomerular filtration rate (eGFR) based on creatinine (eGFRcr), cystatin C (eGFRcys), or their combination (eGFRcr-cys). They used data from the 2021 CKD-EPI external validation cohort, which included 4,050 ambulatory participants (mean age of 57.0 years and mean measured GFR [mGFR] of 76.4 mL/min/1.73m2).2 Defining eGFRdiff as a discordance between eGFRcys and eGFRcr larger than ±15 mL/min/1.73m2, the authors found that 21% of patients had a negative discordance (eGFRcr higher) and 10% had a positive discordance (eGFRcys higher). In both groups, eGFRcr-cys yielded the best performance relative to mGFR, according to bias and P30. The authors acknowledge that their study was limited by the lack of multimorbid or hospitalized patients.