Serum nonmercaptalbumin to total albumin ratio and bilirubin predict ADL decline in older adults with type 2 diabetes

AIMS/INTRODUCTION: To determine whether the ratio of human nonmercaptalbumin to total albumin (HNA%) and serum bilirubin-two oxidative stress-related biomarkers-predicts incident disability in activities of daily living (ADL) among older adults with type 2 diabetes. MATERIALS AND METHODS: In this longitudinal cohort study, we followed 101 adults aged ≥70 years with type 2 diabetes who had no baseline ADL disability. The primary outcome was incident ADL disability requiring long-term care certification, a standardized national system in Japan indicating clinically significant physical impairment. Cox proportional hazards models, restricted cubic splines, and nonparametric bootstrap resampling (1,000 iterations) were used to assess associations. RESULTS: During the 7-year follow-up, 28 participants (27.7%) developed ADL disability. Those who became disabled had higher HNA% and older age, and lower serum bilirubin and albumin at baseline. Restricted cubic splines demonstrated linear increases in disability risk with higher HNA% and linear decreases with higher bilirubin. In the primary multivariable model including HNA%, bilirubin, and age, all remained independent predictors (HNA%: HR 1.063, 95% CI 1.005-1.124; bilirubin: HR 0.740, 95% CI 0.562-0.975; age: HR 1.115, 95% CI 1.032-1.206). This model improved discrimination compared with age alone, demonstrated the lowest Akaike's Information Criterion, and showed good calibration. Bootstrap analyses confirmed the robustness and stability of the model. CONCLUSIONS: Higher HNA%, lower serum bilirubin, and their combined assessment predicted future ADL decline in older adults with type 2 diabetes. These complementary redox biomarkers may contribute to improved risk stratification for functional deterioration.