[Cut-off point of the risk assessment scale for the 9-year risk of functional disability]

Objectives　This study aimed to examine the cut-off point of the Risk Assessment Scale (RAS) for predicting the 9-year risk of functional disability among older Japanese adults.Methods　This prospective, 9-year follow-up study used data from the Sasaguri Genkimon Study in Fukuoka. Of the 2,629 older adults who did not have functional disabilities and participated in the baseline survey in 2011, 2,254 with complete data were included in the analysis. The RAS was assessed using a questionnaire that showed good predictive and external validity for the 3-year risk of functional disability. The outcome was the incidence of functional disability during follow-up, which was defined as a new certification for the need for support or care. The cut-off point of the RAS was estimated as the point indicating the maximum χ² value of the log-rank test. The predictive validity of the RAS for functional disability was examined using C-statistics for the total score, and sensitivity and specificity for the cut-off point, respectively. Participants were then categorized into two groups according to the cut-off point (high-score and low-score groups). Hazard ratio (HR) and 95% confidence interval (95% CI) of the 9-year risk of functional disability for the high-score group compared with the low-score group were calculated using the Cox proportional hazard model. In the multivariate model, HR was adjusted for living alone, education, economic status, drinking, smoking, and multimorbidity.Results　New functional disability was certified in 647 participants (28.7%) during a median follow-up period of 8.75 years. The cut-off point for functional disability was 13/14. The C-statistic was 0.774, and the sensitivity and specificity were 0.726 and 0.712, respectively. Compared to the low-score group (0-13 points), the HR (95% CI) of the high-score group (≥ 14 points) for incident functional disability in 9 years was 5.50 (4.62-6.54) in the crude model, and 4.81 (4.00-5.78) in the multivariate model (P<.001).Conclusion　This study, with its long follow-up period of 9 years, demonstrated that the 13/14 cut-off point of the RAS is suitable for the long-term assessment of functional disability risk. Our results suggest the possibility of using the 13/14 cut-off point of the RAS as a promising tool to grasp the risk of functional disability over a longer time frame, highlighting the potential for early prevention and intervention.