Findings demonstrate that measuring blood pressure (BP) with systematic or random errors could lead to misclassification of high BP for a substantial proportion of US adults.

• Utilizing data from the 2017–2018 National Health and Nutrition Examination Survey (NHANES; n = 5,176), researchers assessed the proportion of US adults that would have their high BP status changed if systolic BP (SBP) and diastolic BP (DBP) were measured with systematic bias and/or random error vs following a standardized protocol.

• High BP was present in 32.0% of the US adults not taking antihypertensive medication.

• Estimates for the proportion with high BP were 44.4% (95%CI: 42.6%,46.2%) and 21.9% (95%CI 19.5%,24.4%) respectively if SBP and DBP were measured with systematic bias, 5 mm Hg for SBP and 3.5 mm Hg for DBP higher and lower than in NHANES.

• High BP was present in 60.6% of the US adults taking antihypertensive medication.

• Estimates for the proportion with high BP were 71.8% (95%CI: 68.3%,75.0%) and 48.4% (95%CI: 44.6%,52.2%) respectively if SBP and DBP were measured 5 and 3.5 mm Hg higher and lower than in NHANES.

• Overall 21.4% of US adults not on antihypertensive medication and 20.5% receiving antihypertensive medication had their high BP status re-categorized if BP was measured with random error, with standard deviations of 15 mm Hg for SBP and 7 mm Hg for DBP.