How Accurate Are Home Blood Pressure Monitors?

Swapnil Hiremath, Interview with:
Swapnil Hiremath
Assistant Professor
Nephrologist, The Ottawa Hospital
Faculty of Medicine at University of Ottawa

Medical Research: What are the main findings of the study?

Dr. Hiremath: Our study was a retrospective analysis of the data from the Nephrology Nurse BP assessment clinic at the Ottawa Hospital. Patients from the nephrology clinic were referred to this clinic not just for validation of their home BP machines, but also for lifestyle education and teaching the correct technique. We validated the monitors brought in by patients using a set protocol (including: confirming equal blood pressure in both arms, measuring BP simultaneously in both arms by an RN using proper technique, taking three resting readings and averaging them).

Firstly, there was a statistically significant difference when we compared the average blood pressure measurement (both systolic and diastolic) values from the home monitor compared to the mercury monitor.

Secondly, when we calculated the proportions of home BP machines that were accurate (using different thresholds of 3 mm, 5 mm and 10 mm Hg difference between home and mercury monitors) a significant proportion of home monitors were inaccurate. These findings have important implications – if clinicians are using data from home monitors to make therapeutic decisions, then some patients may be undertreated – or over treated needlessly.

Medical Research: What was most surprising about the results?

Dr. Hiremath: Surprisingly, when we analysed the data this year, we found a high proportion of patients with discrepancies that would be clinically significant between the office  blood pressure monitors (we use mercury sphygmomanometers) compared to the home BP monitors the patients were bringing in. Looking at the most conservative threshold (a difference of > 10 mm Hg, higher or lower) about 1 in 10 home BP monitors had readings which would be classified as being inaccurate. This study does come with certain caveats, namely that since we had not collected any further details about the monitors themselves (eg year of purchase, model numbers etc) so we cannot comment on the role of these factors.

Medical Research: What should clinicians and patients take away from your report?

Dr. Hiremath: Our suggestion would be that home monitors be validated, ideally by comparing with the ‘gold standard’ i.e. a validated mercury sphygmomanometer, which will need to be done in a doctor’s office. This will be quite challenging, however, in terms of feasibility and logistics – and from insurers’ perspectives.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Hiremath: Though we did find a certain proportion of home BP devices to be inaccurate, we do not yet know the actual reasons for these devices being inaccurate. Eg One could speculate it is wear-and-tear of devices, and if so, how long does it take for that to happen? Should devices be checked regularly – if so how often? The real challenge, of course, is also to show that this matters in terms of real patient centred outcomes. Like any research study, I think we will raise more questions, than answers.


2014 Kidney Week abstract:
Are Home Blood Pressure Monitors Accurate Compared to Validated Devices?