Abstract Body (Do not enter title and authors here): Background:
Hypertension affects approximately 45% of US adults, with an estimated 11–15% of cases undiagnosed. The mortality burden of undiagnosed hypertension has not been well-quantified using recent national data.

Research Question
What is the contribution of undiagnosed hypertension to annual cardiovascular mortality in US adults from 2017 to 2020, and how does its prevalence and impact vary by race, age, and urban-rural residence?

Methods:
We conducted a cross-sectional analysis of NHANES 2017–2020 (n=15,375 adults ≥18 years with blood pressure [BP] measurements) linked to CDC WONDER mortality data (2017–2020, ICD-10 codes I10–I16). Undiagnosed hypertension was defined as measured systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg without self-reported diagnosis (NHANES BPQ050A=2). Population- attributable fraction (PAF) was calculated using a hazard ratio (HR) of 2.1 (95% CI: 1.9–2.3) from the CARDIA cohort (Circulation 2023). Analyses accounted for NHANES complex survey design, excluding participants with missing BP/data (n=1,204, 8.7%). Sensitivity analyses varied HRs (1.8–2.5) and BP thresholds (130/80 mmHg).

Results:
An estimated 13.1% (95% CI: 11.8–14.4%) of US adults had undiagnosed hypertension, with the highest prevalence among non Hispanic Black men aged 18–44 years (27.6%, 95% CI: 24.1–31.1%). Undiagnosed hypertension was associated with 12,400 (95% CI: 10,600–14,200) annual deaths, representing 6.1% (95% CI: 5.2–7.0%) of hypertension-related mortality. Sensitivity analyses yielded 9,100 15,300 annual deaths. Rural residents had 1.7-fold higher odds (95% CI: 1.4–2.0) of undiagnosed hypertension compared to urban residents.

Conclusions:
Undiagnosed hypertension contributes significantly to preventable cardiovascular mortality, disproportionately affecting young Black men and rural populations. Limitations include the cross-sectional design, reliance on single BP measurements, and potential underascertainment of diagnosis status. These findings support universal BP screening at clinical encounters and targeted community outreach to improve hypertension awareness and control.