eGFR–ACR Risk Stratification of Rapid Kidney Function Decline Across Aging Phenotypes in Older Chinese Adults

Objective: To develop an estimated glomerular filtration rate (eGFR) and urine albumin–creatinine ratio (ACR) risk stratification for rapid kidney function decline across aging phenotypes in older adults. Methods: We included 1539 older adults (486 healthy aging, 661 aging with comorbidities, 392 aging with CKD) from the Rugao Longevity and Aging Study and Huashan Hospital. Rapid decline was defined as a ≥ 30% decrease in eGFR over 2 years. We estimated adjusted incidence of rapid decline across baseline eGFR (≥ 90, 75–< 90, 60–< 75, < 60 mL/min/1.73 m 2 ) and ACR (< 30 vs ≥ 30 mg/g) categories within each aging phenotype. We defined adjusted incidence rate of < 5%, 5– 7.5%, 7.5– 15%, and > 15% as no risk, low risk, moderate risk, and high risk, respectively. Random forests assessed the relative contribution of pre-specified eGFR and ACR categories. Results: Mean ages were 77.7 ± 4.4, 78.0 ± 4.1, and 77.7 ± 5.5 years in healthy, comorbidity, and CKD cohort, respectively. Among healthy participants, the adjusted incidence remained in low risk when eGFR was between 60 and 75 mL/min/1.73 m 2 , but increased to moderate risk when eGFR < 60 mL/min/1.73 m 2 . In the comorbidity cohort, a low risk classification was observed with ACR < 30 mg/g and eGFR ≥ 75 mL/min/1.73 m 2 , or with ACR ≥ 30 mg/g and eGFR ≥ 90 mL/min/1.73 m 2 , other combinations were associated with moderate risk. In the CKD cohort, moderate risk corresponded to ACR < 30 mg/g with eGFR ≥ 60 mL/min/1.73 m 2 or ACR ≥ 30 mg/g with eGFR ≥ 75 mL/min/1.73 m 2 , while all other scenarios were classified as high risk. Random forest results corroborated that eGFR dominated discrimination in healthy aging, whereas ACR carried greater weight in comorbidity and CKD cohorts. Conclusion: Phenotype-specific eGFR-ACR thresholds provide pragmatic risk stratification to guide targeted monitoring and earlier intervention in older adults.