The eGFR difference between creatinine-based and cystatin-C-based equations is also important in an Asian population within the J-CKD-DB-Ex

Recent studies have shown that a large negative estimated glomerular filtration rate (eGFR) difference (eGFRdiff), defined as the cystatin C–based eGFR minus the creatinine-based eGFR, is related with kidney events. However, whether this association applies to the Japanese population remains unclear. This study assessed the importance of a negative eGFRdiff in the Japanese population. This was a retrospective cohort study using the J-CKD-DB-Ex. The association between baseline eGFRdiff and kidney composite outcome defined as progression to CKD stage G5 (eGFRcr < 15 mL/min/1.73 m²) or ≥ 40% decline in eGFRcr within 5 years was examined with Cox proportional hazards models. Restricted cubic splines were used to assess nonlinearity. eGFRdiff quartiles were Q1 < − 14.83, Q2 − 14.83 to < − 6.62, Q3 − 6.62 to < 1.72, and Q4 ≥ 1.72 mL/min/1.73 m². Compared with Q3, Q1 was associated with a higher risk of the composite outcome (HR, 2.11; 95% CI 1.24–3.59). Spline analyses showed that hazards increased sharply as eGFRdiff became more negative and were relatively flat around near-zero to positive values. A large negative eGFRdiff was independently associated with a higher risk of kidney disease progression in a Japanese CKD cohort, supporting its use as a prognostic marker.