Diagnosing hypertension

New recommendations

Following an extensive and rigorous literature review,² CHEP is introducing several changes to the recommendations for BP measurement and the diagnosis of hypertension in 2015.¹ New recommendations include the following:

• Routine office BP measurement (OBPM) should be performed using an electronic oscillometric device (level II evidence).

• If a patient has elevated BP readings in the office, a series of standardized out-of-office BP measurements should be performed in order to rule out white-coat hypertension (WCH) and identify those patients who truly have hypertension (level II evidence).

• The out-of-office assessment should preferably be done using 24-hour ambulatory BP measurement (ABPM). A series of measurements with home BP measurement (HBPM) can be done if ABPM is not available or not tolerated by the patient (level II evidence).

• If the average of the out-of-office readings is normal, a diagnosis of WCH is made. Patients with WCH should have their BP assessed annually and should not be treated pharmacologically, although a healthy lifestyle should be encouraged and supported at all times (level II evidence).

A new diagnostic algorithm (Figure 1)² has been developed to reflect these recommendations and is being distributed widely among health care professionals in Canada.

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Figure 1.

Diagnosis of hypertension: Measurement using electronic (oscillometric) upper-arm devices is preferred over auscultation.

ABPM—ambulatory blood pressure measurement, AOBP—automated office blood pressure, BP—blood pressure, DBP—diastolic blood pressure, HBPM—home blood pressure measurement, OBPM—office blood pressure measurement, SBP—systolic blood pressure.

Reproduced from Daskalopoulou et al with permission.²

Blood pressure measurement

Several methods currently exist to measure BP. Manual measurement performed by a clinician using a stethoscope and a mercury or aneroid sphygmomanometer was first introduced in 1896 by Riva-Rocci. Other than the introduction of Velcro for fastening the cuff, this method has changed very little over the past 100 years. Several key studies in the 1940s and 1950s showed a strong correlation between elevated manual BP readings, taken with carefully performed standardized techniques, and increased cardiovascular risk. Unfortunately, more than 30 studies published over the past 3 decades have repeatedly and consistently demonstrated that these standardized techniques are rarely followed in routine clinical practice and, consequently, most auscultatory measurements performed in clinical practice are inaccurate.^3–6 Most frequently these manual readings in the office are higher, but this is not always the case. For these reasons CHEP is recommending that electronic BP measurement is the preferred method for in-office BP assessment.

Electronic BP measurement using the oscillometric technique was introduced in the 1960s and has become ubiquitous in clinical practice. Several organizations have created validation protocols to compare these devices to standardized manual measurements to verify their accuracy.^7,8 Validated devices are now available for clinical use in offices and for 24-hour ambulatory monitoring, as well as for personal use by patients in their homes. These devices eliminate many of the errors that occur when nonstandardized auscultatory measurements are done (rapid deflation, rounding the results, etc). The key advantage of electronic devices is that the measurements are reproducible and accurate when validated.

A specific type of OBPM known as automated office BP (AOBP) measurement utilizes electronic oscillometric devices that are preprogrammed to take a series of readings automatically (3 to 6 readings over 4 to 7 minutes) and calculate an average. When done correctly, the patient is left alone in the room. This technique has been shown to significantly reduce the white-coat effect (P < .001)⁹ and correlate more closely with the criterion standard of 24-hour ambulatory BP daytime average, which in turn correlates well with the risk of adverse cardiovascular outcomes.^9–11

The key differences between these 2 methods of office BP measurement is whether the health care professional remains in the room with the patient during the readings (OBPM) or not (AOBP), and whether multiple readings are automatically performed and averaged (AOBP) or not (OBPM). The upper limit for the AOBP average is 135 mm Hg systolic BP and 85 mm Hg diastolic BP; the upper limit for OBPM is 140 mm Hg systolic BP and 90 mm Hg diastolic BP.

White-coat hypertension

White-coat hypertension occurs when patients have elevated office BP but normal out-of-office BP. Several studies, and meta-analyses of the data in these studies, have shown that patients with WCH have similar cardiovascular risk to normotensive patients.^12,13 Some patients with recognized WCH will go on to develop true hypertension within a few years, but many will remain normotensive.^14,15 The CHEP guidelines recommend that patients with WCH should not be treated with medications¹⁶; however, they should have annual BP measurement and should be encouraged to adopt healthy lifestyle changes when clinically appropriate.

Out-of-office measurement

Over the past several decades, dozens of studies have looked at which method of BP measurement best correlates with clinical outcomes. Ambulatory BP measurement has emerged as the preferred method¹⁷ owing to its many measurements in the patient’s normal environment, as well as its unique ability to measure BP during sleep.^18–21 It requires some technical expertise to ensure the correct cuff is placed accurately, the first reading is checked, and the report is generated. Patients need to attend appointments 2 days in a row for application and removal of the equipment. Finally, some education is needed for clinicians to interpret the report.

When done properly, HBPM is an alternative method for assessing a patient’s out-of-office BP when ABPM is not available or not tolerated by the patient.^22–24 For this purpose, CHEP recommends a series of 2 readings in the morning and 2 readings in the evening for 7 days (ie, 28 total readings). The first day’s readings should be discarded and the average of days 2 to 7 is calculated. The upper limit of normal for the HBPM average is 135 mm Hg systolic BP and 85 mm Hg diastolic BP. It is critical to instruct patients on good BP measurement technique, which includes sitting with the back supported, legs uncrossed with feet on the floor, and the arm supported so the cuff is positioned at heart level. An important difficulty with HBPM is that it can be misreported by patients, so it is important to instruct patients to report all readings as taken without any editing.²⁵ To this end, home BP devices with memories, printouts, or telemonitoring capability are encouraged. Health care professionals play an important role in patient education. Support materials created by CHEP can be found on www.hypertension.ca.

Recommendations in other countries

The CHEP task force is not alone in making these recommendations. In 2011, the National Institute for Health and Care Excellence in the United Kingdom recommended that ABPM be performed for all patients suspected of having hypertension to confirm the diagnosis.²⁶ In December 2014, the US Preventive Services Task Force made the same recommendation.²⁷ Both of these agencies have done extensive literature reviews on both the effectiveness and the cost-effectiveness of this approach. The province of British Columbia has also recently released a clinical practice guideline for hypertension that recommends ABPM to confirm the diagnosis of hypertension.²⁸

Role of family physicians

Canadian family physicians deserve much of the credit for the high rates of treatment and control of hypertension that already exist in Canada. Improvements in diagnostic accuracy are critical to achieving the goal of further optimizing hypertension management, which cannot be accomplished without buy-in from primary care providers. To date, uptake of automated oscillometric AOBP devices within Canadian primary care practices has been relatively high; however, it is not clear if they are being used optimally. The availability of ABPM has been limited owing to cost and lack of reimbursement in many provinces.

In order to achieve the goal of better diagnosis and better control of hypertension, family physicians should be encouraged to invest in both AOBP and ABPM devices and to use them routinely and appropriately in clinical practice. Some provincial health plans already offer reimbursement for ABPM, and efforts are under way in other provinces to establish new billing codes. A “best-practice” table has been created by CHEP to assist providers with performing and interpreting ABPM (Box 1),² as have similar tables for OBPM, AOBP, and HBPM, available from www.hypertension.ca. In many practices the roles of measuring BP, educating patients about HBPM, and administering ABPM are undertaken by nurses and pharmacists; this is another reason for supporting the move to a team-based medical home model for family practice.