Underestimation of Blood Pressure and Stroke Risk by Manual Blood Pressure Measurement

BackgroundHypertension guidelines recommend the use of automated BP devices over manual devices to reduce observer bias, such as terminal digit preference. We aimed to evaluate systematic differences in BP readings and the association with incident stroke according to type of measurement. MethodsUsing de-identified electronic health record data from Optum Labs Data Warehouse from primary care visits in 2024, we classified providers BP measurement method using proportion of odd terminal digit preference as a proxy for manual devices (defined as <0.5% odd digits) and automated devices (defined as 45-55% odd digits). Patients from the manual and automated groups were matched on demographic and clinical covariates. We evaluated cross-sectional BP distributions by measurement modality, and compared mean BP and proportions meeting clinical thresholds using t-tests, and chi squared tests, respectively. In a separate 2019 cohort created using the same methods, we evaluated whether longitudinal associations between systolic BP and incident stroke differ by measurement method. ResultsAmong 336,634 matched patients, mean SBP in the automated group was 131.7 (19.3) mmHg and 125.9 (14.8) mmHg in the manual group. The absolute percentage of patients meeting BP clinical thresholds differed substantially (<130/80: automated 33.2% vs. manual 38.8%; <140/90: automated 61.2% vs. manual 70.9%). Among 686,482 matched patients in the 2019 cohort, the manual group had a 1.16-fold (1.10-1.22) higher risk of stroke at any given BP compared to the automated group. ConclusionManual BP measurement was associated with lower mean BP, BP control, and potential underestimation of stroke risk.