The impact of the Red Blood Cell Distribution Width/Albumin Ratio on All-Cause and Cardiovascular Mortality in Patients with Cardiovascular-Kidney-Metabolic Syndrome: Evidence from NHANES 2009– 2018

Background : The ratio of red blood cell distribution width (RDW) to albumin ratio (RAR) has been demonstrated to have prognostic value in various diseases. However, its association with mortality in patients with Cardiovascular-Kidney-Metabolic Syndrome (CKM) remains unclear. This study aims to investigate the association of RAR with all-cause mortality and cardiovascular mortality in CKM patients. Methods: This study analyzed 10,234 CKM patients from the National Health and Nutrition Examination Survey (NHANES) database for the years 2009-2018. Mortality outcomes were determined based on records from the National Death Index (NDI) as of December 31, 2019. The Cox proportional hazards regression model was used to evaluate the relationship between the RAR and mortality risk. Additionally, this association was further explored using the Kaplan-Meier curve and restricted cubic spline (RCS) models, while adjusting for potential confounding factors. Results: In the study population, the proportions of patients in stages 1, 2, 3, and 4 of CKM syndrome were 23.75%, 60.13%, 5.85%, and 10.27% respectively, with females accounting for 49.58%, and the average age being 49.6 years. After grouping patients by quartiles of RAR levels (Q1-Q4), multivariate Cox regression analysis indicated that compared to the Q1 group, the all-cause mortality risk in the Q4 group increased by 3.12 times (HR=3.12, 95% CI 2.16-4.50, P<0.001), and the cardiovascular mortality risk increased by 2.24 times (HR=2.24, 95% CI 1.21-4.16, P=0.011). For each standard deviation increase in RAR, the all-cause mortality risk increased by 54% (HR=1.54, 95% CI 1.37-1.72, P<0.001), and the cardiovascular mortality risk increased by 52% (HR=1.52, 95% CI 1.30-1.77, P<0.001). Kaplan-Meier analysis confirmed a significantly lower survival rate in groups with higher RAR, and the RCS model further validated the linear positive correlation between RAR and mortality risk. Conclusions: Elevated RAR levels are significantly associated with an increased risk of all-cause mortality and cardiovascular mortality in CKM patients. This finding suggests that RAR could serve as a valuable biomarker for assessing the prognosis of CKM patients, providing a basis for clinical risk stratification and early intervention.