Measurement error adjusted prevalence of undiagnosed hypertension in England: A cross-sectional study

Hypertension case-finding and management is key to reducing premature morbidity and mortality. In England, 14.8% of people receive treatment for hypertension but the total number of hypertensive individuals remains unclear, as it can only be estimated statistically. This study aimed to estimate how many individuals aged 40 + may unknowingly have hypertension by accounting for differences between clinic and out-of-office blood pressure readings.

We analysed individual-level data from the 2017-2019 Health Survey for England (HSE), including individuals aged ≥40 without a hypertension diagnosis. A validated algorithm (Predicting Out-of-Office Blood Pressure- PROOF-BP) was applied to estimate likely out-of-office measurements. Observed BP was defined as the mean of the second and third measurement taken at an HSE visit. Predicted hypertension was calculated using PROOF-BP and observed hypertension using actual clinic measurements. We explored a diagnostic threshold for predicted (out-of-office) hypertension of ≥135/85 mmHg (primary outcome) and of ≥140/90 mmHg (secondary outcome). Weighted hypertension prevalence estimates are presented by age, sex and geographical region. National population statistics were used to extrapolate results to the English population.

The observed prevalence of undiagnosed hypertension in the study population was 27.7% (95% Confidence Interval [CI]:26.4%-29.1%). The predicted prevalence after adjustment was 21.8% (95%CI:20.6%-23.0%). Predicted prevalence was nearly double in males (29.8%, 95%CI:27.8%-32.0%) compared to females (14.6%, 95%CI:13.3%-15.9%) and varied by region: West Midlands (26.3%, 95%CI:22.2%-31.0%), London (16.9%, 95%CI:13.5%-20.9%). Extrapolating estimates to the total population aged ≥40 in England we estimate approximately 4.2 million people in England are unaware of their hypertension. Of these we estimate that over 2.9 million could be newly diagnosed by the current diagnostic pathway.

Over 4 million people in England are estimated to have undiagnosed hypertension. This study's refined analytical approach provides a more precise estimate of this population, supporting targeted public health initiatives to identify and address undiagnosed cases.