PROOF-BP - predicting home blood pressure based on clinical readings
WHAT WE DID:
The diagnosis and management of hypertension depends on accurate measurement of blood pressure in order to target treatment appropriately and avoid unnecessary healthcare costs. Traditionally, blood pressure measurement takes place in the GP’s clinic. However, measurements taken using a 24 hour ambulatory blood pressure monitor are considered more accurate and the GP’s ‘clinic blood pressure’ measurement is often different, leading to incorrect classification and hence inappropriate treatment.
The PRedicting Out-of-OFfice Blood Pressure in the clinic study used characteristics about a patient and their clinic blood pressure level to derive a prediction model (a mathematical equation which permits prediction of an outcome) for the difference between clinic and 24 hour ambulatory blood pressure. We analysed data from more than 2000 patients, looking at factors including age, gender, body mass index, alcohol consumption and tobacco use. We also studied a number of ‘blood pressure characteristics’ from multiple readings taken in the clinic, including the difference between the first and last readings and the rate of change in blood pressure among others. Data from around 900 patients were used to build a model, identifying factors that affected the difference between home and clinic blood pressure readings. The model was then validated by checking against the data from the other patients in the study.
This approach has the potential to save large amounts of money for the NHS by avoiding unnecessary treatment in those with the white coat effect. It may also lead to fewer patients suffering from heart attacks and stroke, by treating patients' blood pressure more effectively - Dr James Sheppard, University of Oxford
The result is a prediction model that uses three separate blood pressure readings taken in a single consultation and basic patient characteristics to give an adjusted blood pressure reading that is significantly more accurate than existing models for identifying hypertension. The model correctly classified hypertensive status in 93% of cases, compared to the next best, the NICE guidelines, which correctly classified 78% of patients.
Where can I find out more?
This research was published in the scientific journal Hypertension and can be found here . Follow-up work examined the cost-effectiveness of using the approach to diagnose hypertension showing it to be better than existing strategies and this work was published here. Further validation work has been undertaken and this is detailed here.
The equation is available as an online calculator for health professionals at https://sentry.phc.ox.ac.uk/proof-bp/.