Blood pressure (BP) has been measured as office BP, usually taken after 5 min of quiet rest, in all clinical outcome trials in hypertension until recently when the Systolic Blood Pressure Intervention Trial (SPRINT) was carried out. In the publication of the main SPRINT results, it was not evident how BP had been measured . Following some literature search , it became visible that BP in SPRINT was taken as unattended automated office blood pressure (unattended-AOBP). The more than 100 sites participating in the SPRINT Study in the USA [1,2] used the Omron 907 automated model (Omron Healthcare, Lake Forest, Ilinois, USA). Personnel were additionally trained to use the full capacity of this device by leaving the room prior to the 5 min period of rest followed by the preset unattended automated measurements at 5, 6 and 7 min. This is properly described in later publications including in the article reporting the subgroup data in the elderly participants  though a post hoc investigation in response to the debate  suggested that not all investigators had followed the protocol and left the room prior to BP measurement , or maybe some of the SPRINT investigators years later did not remember how their personnel had performed the BP measurement .
The SPRINT study was designed to compare outcomes in hypertensive people with high cardiovascular risk who were randomized to target office SBP less than 120 mmHg vs. less than 140 mmHg. However, until the method for BP measurement in SPRINT was clarified in detail , that is, the unattended approach, there was uncertainty, which BPs had been compared in the SPRINT Study. A 24-h ambulatory BP (AMBP) sub-study in SPRINT participants was particularly useful in this context ; it could be calculated that in SPRINT, the investigators compared office SBP of approximately 132 vs. 144 mmHg when translated from the unattended-AOBP. This calculation was done, as recommended in European Hypertension Guidelines, by adding 5 mmHg to the daytime ambulatory SBP measured in the SPRINT sub-study .
A controversy regarding, which method that had been used for office BP measurement in a large outcome trial like SPRINT [1–5] initiated further investigations of the relationships between BP taken in the office manually or with semi-automated or automated device like the Omron 907, unattended-AOBP and AMBP [6–10]. In this issue of Journal of Hypertension, Seo et al. report from South Korea, a study, which aimed to compare unattended-AOBP with ABPM in patients with a high cardiovascular risk. Participants (n = 1208) were recruited from a prospective cohort study (Cardiovascular and Metabolic Disease Etiology Research Center–High Risk Cohort), and they had successfully undergone both unattended-AOBP and ABPM within 7 days of enrollment. Unattended-AOBP was taken with a validated device (HEM 7080-IC; Omron, Kyoto, Japan) and so was 24-h AMBP (Takeda TM-2430 instrument; A&D Medical, Tokyo, Japan). The 95% limits of agreement between systolic unattended-AOBP and daytime systolic ABPM were −34.8 and 20.2 mmHg (mean difference = −7.3 ± 14.0). The mean differences in quintiles of unattended-AOBP distributions increased with decreasing systolic unattended-AOBP (Table 1). The prevalence of masked hypertension was 310 (25.7%) and that of white-coat hypertension was 102 (8.4%). Cut-offs here were less than or a least 135/85 mmHg and the terms ‘masked’ and ‘white-coat’ were used because no better terms are available to characterize the differences between unattended-AOBP and AMBP. The lower range of systolic unattended-AOBP exhibited a large discrepancy with daytime systolic ABPM. Moreover, higher cardiovascular risk and history of asymptomatic cardiovascular disease were independently associated with larger discrepancy between unattended-AOBP and ABPM. The authors concluded that the status of BP control should be confirmed using out-of-office BP measurements, even when using unattended-AOBP as a clinical BP reference in high-risk patients.
The key finding in this study was the relatively large difference and poor limits of agreements compared with similar data in early reports [12–14]. The inconsistent findings may be because of differences in populations; the early studies [12–14] may to a large extent have investigated people with mild hypertension referred for AMBP, whereas the present  and some other recent studies have included people with high-risk hypertension and hypertensive people being well treated with antihypertensive drugs. The present study thus showed that the discrepancy was larger in people with higher cardiovascular risk and more asymptomatic cardiovascular disease. The lower the unattended-AOBP, the larger the discrepancy and it may be tempting to speculate that the BP reactivity is larger in people with more advanced cardiovascular disease. In other words, the higher cardiovascular risk and the more subclinical disease, the larger is the potential for these people to have a decrease in BP when they are seated completely unattended and by themselves during standard quiet conditions in the clinic to have their BP taken with a preset automated device. Such conditions may be extended beyond the clinic or the physician's office: ‘Being alone and not location is what matters most’ .
Thus, it matters how BP is measured. Office BP taken manually, with semi-automated or even with automated device  has been the standard in all outcomes trials in hypertension research until the SPRINT study  came about. Typically, study participants have been seated quietly for 5 min before measurements. This standardization of BP measurements has been a major achievement for research. There are minor differences in the way measurements have been done and reference values have been extracted (waiting time, average of three measurements, average of last two measurements, etc.), but basically the same method has been used all over the world, which is a treasure for hypertension research. We can just imagine what it will mean in the future to have articles adopting SPRINT and other classical measurements, with no possibility to compare.
The novelty with BP measurements in SPRINT was the unattended approach, which was a part of the protocol followed by a large group of investigators but not necessarily by all . SPRINT was an outcome trial, which searched for the optimal target SBP in high-risk hypertensive people . SPRINT, like the present study by Seo et al., showed a large discrepancy between unattended-AOBP and AMBP  probably because patients were of the high-risk category, and thus similar to the patients in the study by Seo et al.. We have been critical to an approach like this in the investigation of the optimal target office BP in the treatment of hypertension . The main reason for our criticism  is that many patients will be treated to unexpectedly low-target BPs when unattended-AOBP is used; they may get adverse events because of hypotension, and subsequently they may discontinue treatment and remain unprotected from antihypertensive treatment.
In addition, unattended-AOBP has limited documentation in predicting cardiovascular disease. To our knowledge, observational data is limited to one prospective study in Canada in which unattended-AOBP was taken in pharmacies . There was a relationship with cardiovascular disease but the relationship was not very strong . Because of widespread use of unattended-AOBP, it could even cause a concern that BP is underestimated in the Canadian population [18,19]. It could then be argued that BP could rather be taken during a short (6 min) bicycle exercise test at a moderate load like 100 W; an early rise in SBP in this setting is a strong predictor of coronary disease and cardiovascular death  even when adjusted for BP at rest and other cardiovascular risk factors. But there is no randomized intervention trial to support using exercise BP as basis for treatment in clinical practice – much like AMBP, home BP and the unattended-AOBP. The conclusion is then that in clinical practice, we should measure office BP measurements with physician or personal being present during measurements, manually or with semi-automated or automated device. All other methods for measurements of BP should be supplementary, whichever method we may believe in when we assess cardiovascular risk.
Conflicts of interest
S.E.K. has received lecture and consulting honoraria from Bayer, Merck & Co., Sanofi and Takeda. G.M. reports no relevant conflicts of interest to this commentary.
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