Blood Pressure Measurement—Following a Standardized Protocol Is What Matters

Many patients have different blood pressure (BP) levels when measured in the office setting versus outside of the office setting. White coat hypertension, defined by BP in the hypertensive range when measured in the office setting but not in the hypertensive range when measured outside of the office, was first described in the 1980s.1 Over the past four decades, a number of studies have evaluated the prevalence of, and outcomes associated with, white coat hypertension. A meta-analysis published in 2019 estimated white coat hypertension to be associated with a 36% higher risk (hazard ratio [HR] 1.36; 95% CI 1.03–2.00) for cardiovascular events compared to sustained normotension, defined by non-hypertensive BP levels when measured in the office and outside of the office setting.2 The excess risk for cardiovascular events associated with white coat hypertension was substantially less than the risk associated with sustained hypertension, defined by having BP in the hypertensive range when measured in and outside of the office setting (HR 2.31; 95% CI 1.91–3.15).3 Also, white coat effect, the term used for white coat hypertension among individuals taking antihypertensive medication was not associated with an increased risk for cardiovascular events (HR 1.12; 95% CI 0.91–1.39) when compared with sustained controlled BP, the term used for sustained normotension among individuals taking antihypertensive medication.2 Consistent with no or only a modest increase in cardiovascular risk associated with white coat hypertension versus sustained normotension and white coat effect versus sustained controlled BP, the 2017 American College of Cardiology/American Heart Association (ACC/AHA) BP guideline recommends the initiation and intensification of antihypertensive medication be delayed among individuals with these phenotypes.4 The 2017 ACC/AHA BP guideline recommends measuring BP outside of the office setting to identify white coat hypertension among adults with office systolic BP (SBP) of 130 to 159 mmHg or office diastolic BP (DBP) of 80 to 89 mmHg. Screening for white coat effect is recommended for adults taking three or more classes of antihypertensive medication with office SBP of 130 to 139 mmHg or office DBP of 80 to 89 mmHg. An analysis of the US National Health and Nutrition Examination Survey estimated that among US adults with SBP ≥ 130 mmHg or DBP ≥ 80 mmHg, 93% of those not taking and 13% of those taking antihypertensive medication are recommended out-of-office BP monitoring by the 2017 ACC/AHA BP guideline to screen for white coat hypertension and white coat effect.5 This equated to almost 50 million US adults.5 Numerous barriers to out-of-office BP monitoring have been reported by clinicians and patients, leading researchers to search for approaches to rule out the presence of white coat hypertension and white coat effect without the need for conducting out-of-office BP monitoring.6 Despite decades of research, the reasons people have white coat hypertension and white coat effect are not entirely clear. One reason that has been hypothesized is an alerting effect that some people experience while someone is measuring their BP. In the 1990s, fully automated oscillometric BP measurement devices became available that are capable of taking multiple readings without a person being present.7 From this perspective, BP measurement in the office setting using an automated device without medical staff present has been suggested to reduce alerting effects.8 Additionally, alerting effects may be reduced by having a longer rest period before BP is measured in the office setting. Although the white coat effect is not likely to be entirely eliminated, a reduced alerting effect may produce BP readings in the office setting that are closer to out-of-office measurements. In the current issue of the American Journal of Hypertension, Green and colleagues present results from a rigorous study testing if BP levels are different when measured unattended versus attended and after a 15-min versus 5-min rest period.9 The investigators randomized 133 participants with SBP ≥ 140 mmHg or DBP ≥ 90 mmHg, without a prior hypertension diagnosis and who were not taking antihypertensive medication, to have their BP measured three times unattended and then three times attended or three times attended and then three times unattended. Additionally, SBP and DBP were measured after a 5-min and 15-min rest period. Using the average of the three readings from each set, the primary outcome was the within-person difference in SBP and DBP when measured attended versus attended. Additionally, the sensitivity and specificity for identifying white coat hypertension based on out-of-office BP levels on ambulatory blood pressure monitoring (ABPM) was evaluated. In this study, there was no evidence of a difference in SBP or DBP when measured unattended or attended. Specifically, the difference, attended minus unattended, in SBP was 0.14 mmHg (95% CI: –0.78 to 1.06) and in DBP was 0.16 (95% CI: −0.45 to 0.78). Additionally, office BP when measured without a person present had sensitivity of 71.0% and specificity of 56.8% for identifying awake hypertension on ABPM. The authors concluded that having a person present versus not present when BP is measured in the office setting (i.e., attended versus unattended measurements) had little effect on mean SBP or DBP. The study by Green adds to a growing body of evidence that unattended and attended BP measurements are virtually identical when measurements are performed following a standardized protocol by trained staff.10 The protocol used by Green and colleagues included several steps that may have avoided the inaccurate measurement of BP. Of particular importance to attended office BP measurements, staff and study participant did not talk during the rest period or while measurements were being obtained. Talking during the BP measurement procedure has been estimated to increase SBP by 4 to 19 mmHg and DBP by 5 to 14 mmHg.11 An analysis of US National Health and Nutrition Examination Survey data estimated a systematic bias of 5 mmHg higher SBP and 3.5 mmHg higher DBP could increase the proportion of US adults not taking antihypertensive medication with SBP ≥ 130 mmHg or DBP ≥ 80 mmHg by 12.4% (95% CI: 10.6%, 14.5%).12 Therefore, ensuring that patients or medical staff are not talking during the BP measurement procedure is very important. While the 2019 AHA Scientific Statement on BP Measurement did not provide definitive advice on whether BP should be measured unattended or attended, it suggested that to ensure patients and staff are not talking, measuring BP unattended may be preferred.13 A second aspect of the study by Green and colleagues was the evaluation of SBP and DBP when BP was measured after a 15-min rest period versus 5-min rest period.9 The authors hypothesized that the length of the rest period may have a differential effect on SBP and DBP levels. The difference in BP was very small when measured after a 15-min rest period versus a 5-min rest period (ΔSBP = −0.45 [95% CI: −1.36, 0.47] and ΔDBP = 0.61 [95% CI: −1.23, 0.00]). The finding of a small difference in SBP or DBP when measured after 15 min versus 5 min of rest is consistent with two recent studies that randomized participants to have their BP measured after different rest periods. Brady and colleagues randomized 113 adults to have their BP measured after no rest, 2 min of rest, and 5 min of rest. In this study, SBP and DBP were within 2 mmHg of each other, whether measured after no rest (127/74 mmHg), 2 min of rest (127/74 mmHg), or 5 min of rest (128/75 mmHg).14 In a separate study, 618 participants were randomized to no rest or a 5-min rest prior to having three BP measured three times. The mean SBP/DBP was 141/83 and 138/82 in the no rest and 5-min rest groups, respectively. In this latter study, ABPM was conducted and awake SBP and DBP were closer to office SBP and DBP without a rest period versus after a 5-min rest period.15 Not having a rest period may facilitate the implementation of a standardized BP measurement protocol. However, replication of these studies in populations more representative of routine clinical care is needed before a standardized BP measurement protocol without a rest period is implemented. In summary, the study by Dr. Green provides important new data to inform the accurate measurement of BP. Results from this study should provide clinicians and health systems confidence that if a standardized protocol is being followed, without talking during the BP measurement procedure, the office BP values will be similar whether measured attended or unattended. The low sensitivity and specificity of unattended office BP indicates that out-of-office BP needs to be conducted when white coat hypertension is suspected. Additionally, a rest period longer than 5 min will not produce different SBP or DBP values when compared with a 5-min rest period. The importance of accurately measuring BP has been emphasized for more than 80 years, yet it is not being done.16,17 The analysis by Green and colleagues should encourage clinicians to measure BP carefully, following a standardized protocol, without concern for it being done with someone in the room.