Office blood pressure is lower than awake ambulatory blood pressure at lower targets for treatment

The traditional approach to the diagnosis and management of hypertension has been based on manual office blood pressure (BP), most often recorded using a mercury sphygmomanometer. However, the dominance of manual office BP has been challenged by studies which have conclusively shown that 24‐hour ambulatory BP monitoring (ABPM) and home BP are better predictors of the cardiovascular risk associated with hypertension than office BP.1, 2 As a consequence, evidence‐based guidelines3, 4 now recommend ABPM or home BP for diagnosing hypertension, with the diagnostic threshold for a normal BP being <135/85 mm Hg for awake ambulatory BP and home BP compared with 140/90 mm Hg for conventional office BP.

However, manual office BP is still used to assess the BP status of most patients after the initiation of drug therapy, unless home BP is also being recorded. ABPM is rarely repeated if the manual office BP decreases below 140/90 mm Hg with treatment, since the patient is then considered to have normotension. Masked hypertension while on treatment is still a concern, but there is not yet enough evidence to support the routine use of ABPM to detect it.

Paradoxically, manual office BP is not sufficiently accurate to diagnose hypertension and initiate therapy, but it is still considered to be adequate for monitoring the response to therapy. As long as the target BP was <140/90 mm Hg, little attention was given to this paradox. However, the publication of several randomized controlled trials5, 6, 7 examining lower vs higher office BP targets for the treatment of hypertension has increased interest in the benefits and risks of lowering systolic BP to values <120 to 130 mm Hg. Each of these studies used a validated oscillometric sphygmomanometer designed for office use to record a mean of several office BP readings.

The ensuing controversy about the optimal target for therapy has been further complicated by the technique used to record BP in SPRINT (Systolic Blood Pressure Intervention Trial): automated office BP (AOBP). AOBP involves the use of a fully automated oscillometric sphygmomanometer that is capable of taking multiple BP readings with the patient resting quietly and alone. Although the protocol for SPRINT7, 8 did not clearly specify that the multiple, automated BP were to be recorded with the patient resting alone, the readings in SPRINT were either AOBP or very well‐performed, multiple, oscillometric BP measurements. If office BP is to be the target for antihypertensive therapy, it would be of interest to know more about the different techniques for its measurement and the relationship of their readings to the gold standard of awake ambulatory BP.

1. TECHNIQUES FOR RECORDING OFFICE BP

Office BP can be measured in accordance with established guidelines, using either manual or oscillometric sphygmomanometers. These methods were used in landmark research studies in hypertension and have formed the basis for both the diagnosis and management of hypertension in clinical practice. However, studies9 comparing these “research‐quality” readings with office BP in the community have reported that the routine office BP used for patient management is, on average, 10/7 mm Hg higher. These routine office BP readings are also less accurate, being subject to a white‐coat effect, digit preference (rounding off values to the nearest zero), and poor adherence to BP measurement guidelines.10

With the ongoing disappearance of the mercury sphygmomanometer because of environmental concerns, manual office BP is now synonymous with use of the aneroid device, a technique that was previously criticized because of the potential for loss of accuracy caused by infrequent recalibration.11, 12 Although other nonmercury sphygmomanometers are available for recording BP manually, the use of these devices in office practice is currently limited. Oscillometric recorders have become more popular for office use, with AOBP now the preferred method for office BP measurement in Canada.13 The advantages of AOBP have also been recognized in other hypertension guidelines.14, 15

2. HOW DOES OFFICE BP RELATE TO ABPM?

The threshold for defining hypertension using office BP (140/90 mm Hg) is higher than that of the awake ambulatory BP (135/85 mm Hg). Most studies comparing the two methods for BP measurement have reported that office BP is higher than the ambulatory BP, as noted in a recent review by Parati and colleagues.16 However, this relationship may not be present at lower levels of BP, such as in the range of systolic office BP <130 mm Hg examined in the ACCORD (Action to Control Cardiovascular Risk in Diabetes), SPS3 (Secondary Prevention of Small Subcortical Strokes), and SPRINT trials.5, 6, 7

In 1993, Staessen and colleagues17 reviewed 30 studies in which conventional office BP readings were compared with daytime ambulatory BP. In untreated patients with borderline (n=719) or definite (n=1773) hypertension, the mean office BP was 12/2 and 20/1 mm Hg, respectively, higher than the corresponding mean daytime ambulatory BP (Table). However, in 4577 untreated patients with a normal office BP, mean (±standard deviation) office BP was 119±12/73±9 mm Hg compared with a mean daytime BP of 122±11/85±12 mm Hg. The only data (Table) comparing AOBP and awake ambulatory BP in untreated patients with an office systolic BP <130 mm Hg were obtained in 57 referrals for 24‐hour ABPM.18 In this population, mean AOBP was 123±7/78±9 mm Hg compared with a mean awake ambulatory BP of 126±9/78±9 mm Hg (P=.009). Thus, in untreated patients with a mean office systolic BP <130 mm Hg, the mean awake ambulatory BP seems to be higher, and not lower, than the mean office BP.

Table 1.

Office BP, AOBP, and awake ambulatory BP for patients with a systolic office BP <130 mmHg

Study (reference)	Population	Treated, %	No.	Office BP, mm Hg	AOBP, mm Hg	Ambulatory BP, mm Hg
Staessen17	Data from 30 studies	0	4577	119±12/73±9		122±11/75±8
de la Sierra19	Family practice registry	100	921	111±7/70±11a		118±12/71±9
Myers18	Referrals for ABPM	0	57		123±7/78±9b	126±9/78±9
Godwin21	Family practice	100	207		121±7/74±9c	132±10/77±7
Myers22	Family practice	97	124		119±7/72±9c	129±10/73±8
SPRINT‐ABPM20	Clinical trial target BP <120 mm Hg	100	453		120±13/66±11	127±12/72±9

Abbreviations: ABPM, ambulatory blood pressure monitoring; AOBP, automated office blood pressure; BP, blood pressure; SPRINT‐ABPM, Systolic Blood Pressure Intervention Trial–Ambulatory Blood Pressure Monitoring arm.

^aOscillometric sphygmomanometer.

^b P=.009.

^c P<.001.

Patients with treated hypertension also appear to have office BP readings that are lower than the awake ambulatory BP in the lower part of the normal BP range (Table). In 921 patients treated for hypertension in primary care in Spain who had a systolic office BP <120 mm Hg, the mean office BP was 111±7/70±11 mm Hg compared with an awake ambulatory BP of 118±12/71±9 mm Hg.19 The office BP readings in this study were obtained using an oscillometric sphygmomanometer, with readings recorded in the presence of physicians or nurses. Having BP data from routine office practice is important, since this is the setting where both the screening for hypertension and its diagnosis are made. Moreover, BP readings in primary care in the community are strongly influenced by the white‐coat effect, being, on average, 10/7 mm Hg higher than manual BP readings recorded according to guidelines in research studies.9 In the Spanish study,19 the overall mean office BP in 39 132 patients was 151/88 mm Hg compared with a mean daytime ambulatory BP of 131/79 mm Hg. This marked white‐coat effect is the opposite of what was seen in the subgroup of patients with an office systolic BP <120 mm Hg, who had a mean office BP 7/1 mm Hg lower than the mean daytime ambulatory BP. The one comparison between office BP and ambulatory BP for which data are not available for the lower normal BP range is the relationship between BP recorded in routine office practice using a manual sphygmomanometer and ambulatory BP.

Similar differences between office BP and ambulatory BP have been seen in treated patients when the office BP was recorded using the AOBP technique (Table). In the SPRINT ABPM substudy,20 mean office BP was 120±13/66±11 mm Hg compared with a mean awake ambulatory BP of 127±12/72±9 mm Hg. In 207 treated patients recruited from the practices of family physicians in the community21 who had a systolic AOBP <130 mm Hg, mean AOBP was 121±7/74±9 mm Hg compared with an awake ambulatory BP of 132±10/77±7 mm Hg (P<.001). In this study, a Bland‐Altman plot showed a negative slope, with the individual data points displaying a higher ambulatory BP vs AOBP in the systolic BP <130 mm Hg range.

In another group of 124 patients with treated hypertension recruited from family practices in the community22 with a systolic AOBP <130 mm Hg, mean AOBP was 119±7/72±9 mmHg compared with an awake ambulatory BP of 129±10/73±8 mm Hg (P<.001).

Parati and colleagues16 have also noted that office BP in treated patients in the European Lacidipine Study on Atherosclerosis (ELSA) study became lower than the 24‐hour ambulatory BP at a threshold of about 115 to 117/70 to 73 mm Hg, which is consistent with the other comparisons between office BP and awake ambulatory BP.

3. IMPLICATIONS FOR TARGET BP

ABPM is recognized as being a stronger predictor of cardiovascular risk than office BP. In clinical practice, office BP is associated with a white‐coat effect, with readings being considerably higher than awake ambulatory BP. A closer examination of the relationship between office BP and awake ambulatory BP suggests that a white‐coat effect is not a concern in patients with a systolic BP <130 mm Hg. The technique for recording BP is especially important when using office BP to screen for hypertension. Routine manual office BP is associated with a white‐coat effect, whereas AOBP readings are similar to the awake ambulatory BP. At a target systolic BP <130 mm Hg, AOBP, attended oscillometric office BP, and manual office BP performed according to guidelines all appear to be devoid of a white‐coat effect. However, there are no data on the occurrence of white‐coat effect in this BP range when using manual BP in routine office practice. Considering the increasing popularity of all types of oscillometric sphygmomanometers in clinical practice, it may not matter whether BP readings are taken with or without medical staff being present when systolic BP is <130 mm Hg. Since BP thresholds and targets for treatment are both important, it is time to focus more research on target BP and how to best record readings in the lower part of the normal range. ABPM may not be required when lower BP readings are less subject to a white‐coat effect.

4. CONCLUSIONS

The relationship between office BP and awake ambulatory BP appears to be different at the thresholds for diagnosing hypertension than at target BP in the lower part of the normal range. Regardless of their treatment status, patients with mean office systolic BP <130 mm Hg generally have a lower office BP value than the corresponding awake ambulatory BP. The difference appears to be somewhat greater in patients with treated hypertension, which is consistent with the finding that antihypertensive therapy tends to lower office BP more than it does ambulatory BP.16

The preferred method for making a diagnosis of hypertension is 24‐hour ABPM or home BP. When it comes to the target BP for drug therapy in routine office practice, either AOBP or attended oscillometric BP measurement may be used. Manual office BP may also be suitable for evaluating target BP, although there are currently no data to support its use for this purpose in routine office practice.

CONFLICTS OF INTEREST

The authors have no conflicts of interest to declare.

Myers MG, Kaczorowski J. Office blood pressure is lower than awake ambulatory blood pressure at lower targets for treatment. J Clin Hypertens. 2017;19:1210–1213. 10.1111/jch.13090