Red cell distribution width-to-albumin ratio and hypertension risk: age-specific threshold effects identified in the 2017–2020 NHANES U.S. Adult population

Background As a major modifiable risk factor for cardiovascular diseases worldwide, hypertension novel biomarkers that integrate inflammatory and metabolic pathways may improve risk stratification. The association between the red cell distribution width-to-albumin ratio (RAR), a newly identified inflammatory biomarker, and hypertension has not been systematically evaluated in population-based studies. Methods A cross-sectional study included 7,878 adults. Weighted multivariable logistic regression and threshold effect models were employed to analyze nonlinear associations, with subgroup analyses exploring heterogeneity. Results RAR showed a linear positive association with hypertension (adjusted OR = 1.26 per unit, 95%CI:1.09–1.44, P < 0.05), a threshold effect was observed. Piecewise regression revealed a significant association when RAR ≥ 3.4, with a higher hypertension prevalence (adjusted OR = 1.34, 95%CI:1.17–1.54), while no association existed below 3.4 ( P = 0.408). For those aged 40–60 years, the inflection point was RAR = 3.92 (95%CI:3.76–4.51), with stronger associations observed below this threshold (OR = 1.80, 95%CI:1.33–2.43). Subgroup analyses revealed significant heterogeneity: diabetics exhibited stronger associations than non-diabetics (interaction P = 0.02), and enhanced associations were also observed in females and individuals aged > 40 years. Conclusion This study confirmed a linear positive correlation between red blood cell distribution width and albumin ratio (RAR) and the prevalence of hypertension, RAR ≥ 3.4 was associated with higher hypertension prevalence and may help identify high-risk subgroups, particularly among diabetics, but its predictive value warrants validation through prospective cohort studies.