Monday, April 24, 2017

Rethinking how we use office blood pressure measurements

- Jennifer Middleton, MD, MPH

The accuracy of medical office blood pressure (BP) measurements is coming under increased scrutiny, possibly affecting how we treat our patients. Basing hypertension diagnosis and treatment on the BP values we obtain in our offices is routine for many of us as family physicians, but checking BP several times during an office visit may more appropriately guide diagnosis and treatment decisions.

In its March/April issue, the Annals of Family Medicine includes a study on "Thirty-Minute Office Blood Pressure Monitoring in Primary Care." The researchers examined every patient over a six-month period who received automated office BP monitoring over a 30 minute period (OBP30) in a practice in the Netherlands. This method has been previously studied there and was found to yield more useful BP data than a single measurement. The researchers then compared the OBP30 readings to these same patients' previously obtained single BP measurements and asked their physicians if they found a clinically meaningful difference: did they make different diagnosis and treatment decisions because of the OBP30 readings?

There were clinically significant differences in both systolic and diastolic BP comparing the single office BP measurement with the OBP30 measurements; the mean systolic OBP30 measurement was 22.8 mmHg lower than the single office BP measurement (95% CI, 19.8–26.1 mm Hg), and the mean diastolic OBP30 measurement was 11.6 mmHg lower (95% CI, 10.2–13.1 mm Hg). The physicians stated that they would have initiated or intensified BP treatment in 79% of patients based on the single office BP measurement, compared to only initiating or intensifying treatment in 25% of these same patients once they had their OBP30 measurements.

These sizable differences imply that we are at risk of overtreating, and possibly incurring undesirable medication side effects, if we base decisions only on single office BP measurements. SPRINT already encourages more aggressive BP goals in some patients; if aiming for a BP of less than 120/80, the risk of over-treatment could be magnified if medication increases are made solely based on solitary BP readings. Additionally, a study reviewed in the current AFP article on "Severe Asymptomatic Hypertension: Evaluation and Treatment" cites a study finding that "[i]n more than 30% of patients with severe asymptomatic hypertension, blood pressure lowers to an acceptable level (mean of 160/89 mm Hg) without intervention following a 30-minute rest period." Even when BPs are first alarmingly high, waiting and rechecking can prevent over-treatment.

An editorial accompanying the above Annals article reviews the challenges of changing our office workflow to accommodate improved BP measurements. Allowing a patient to sit for even 5 minutes before a single BP measurement can be a challenge, let alone keeping them there for 30 minutes. Dr. Lin has written previously on the blog about the usefulness of home BP measurements in adjusting treatment in patients with established hypertension, so that might be an alternative. Either way, if our goal is to treat the patients who need treatment - and not treat those who don't - expanding beyond a single office BP measurement to guide our decisions may help.

There's an AFP By Topic on Hypertension which includes several resources to assist with diagnosis and treatment if you'd like to read more. This recent Family Practice Management article on "Improving Blood Pressure Control with Strategic Workflows" might also be of interest.

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