Nonlinear association between the erythrocyte distribution width-to-albumin ratio and mortality in older adults: A retrospective cohort study using NHANES 1999 to 2018 data

Older adults face high risks of all-cause and cardiovascular disease (CVD) mortality; however, simple, inexpensive biomarkers for early risk identification are limited. The red cell distribution width-to-albumin ratio (RAR) is a low-cost, routinely measured marker, but its prognostic value in older adults is unclear. We examined whether RAR is independently associated with all-cause and CVD mortality in older adults. We conducted a retrospective cohort study using data from the United States National Health and Nutrition Examination Survey (1999-2018). The study included 16,558 adults aged ≥60 years, with median follow-up of 9.4 years. Multivariable Cox proportional hazards models estimated associations between RAR and mortality. Nonlinearity was evaluated using generalized additive models with penalized splines and two-piecewise Cox models combined with a recursive algorithm. Among 16,558 participants (mean age 70.7 ± 7.3 years; 49.8% men), RAR quartiles were Q1 (2.32-2.95), Q2 (2.95-3.16), Q3 (3.16-3.45), and Q4 (>3.45). Over a median 9.4-year follow-up, 6119 deaths occurred, including 2048 CVD deaths. In fully adjusted models, RAR was associated with greater risks of all-cause mortality (hazard ratio = 2.15, 95% confidence interval = 1.89-2.45) and CVD mortality (hazard ratio = 2.05, 95% confidence interval = 1.74-2.41). Associations were nonlinear, with a threshold at RAR = 4.05; below this level, higher RAR was linked to increased all-cause and CVD mortality, whereas above it, the association weakened and CVD mortality risk plateaued. RAR was independently and nonlinearly associated with all-cause and CVD mortality in older adults. These findings support RAR as a simple biomarker for mortality risk identification in older adults.