Hemoglobin to red blood cell distribution width ratio and mortality among U.S. adults with diabetes or prediabetes: a nationwide population-based cohort study

Background: The hemoglobin (Hb) to red blood cell distribution width (RDW) ratio (HRR) has emerged as a novel marker associated with various diseases and poor prognosis. However, its relationship with all-cause and cardiovascular mortality among individuals with diabetes or prediabetes remains unclear. Methods: This population-based prospective cohort study analyzed data from the National Health and Nutrition Examination Survey (NHANES) from 2001 to 2018, with mortality follow-up through 2019. All-cause and cardiovascular mortality were the primary outcomes. Weighted multivariable Cox proportional hazards models were applied to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between HRR and mortality. Restricted cubic spline analyses were conducted to assess potential nonlinear relationships, and segmented Cox models were applied to estimate HRs and 95% CIs on either side of the identified inflection points. Results: This study included 18,017 U.S. adults (≥ 20 years) with diabetes or prediabetes. Over a median follow-up of 8.2 years, 3,380 all-cause deaths and 1,091 cardiovascular deaths occurred. Higher HRR was independently associated with lower all-cause (HR = 0.10, 95% CI: 0.07–0.14) and cardiovascular mortality (HR = 0.08, 95% CI: 0.05–0.13). Restricted cubic spline analyses revealed L-shaped inverse associations, with inflection points at 1.00 and 1.08 for all-cause and cardiovascular mortality, respectively. The L-shaped pattern persisted among participants with diabetes, whereas a linear relationship was observed in those with prediabetes; subgroup, interaction, and sensitivity analyses confirmed these findings. Conclusions: In this national cohort study, HRR exhibited a significant L-shaped association with all-cause and cardiovascular mortality among U.S. adults with diabetes or prediabetes. These findings suggest that HRR may serve as a promising predictor for identifying individuals at increased mortality risk in clinical practice.