INTRODUCTION

Several groups, including the United States Preventive Services Task Force (USPSTF), recommend the use of out-of-office blood pressure (BP) to confirm a diagnosis of hypertension.1,2,3,4,5 BP can be measured in out-of-office settings using home BP devices or 24-h ambulatory blood pressure monitoring (ABPM). Patients’ acceptance and adherence to different methods of BP measurement are also important when developing guidelines for clinical practice.

The acceptability of different methods of BP measurement for making a new diagnosis of hypertension has been evaluated in several studies over the last 18 years.6,7,8,9,10 These have found that measurement in the office (by a health care professional) or at home is consistently more acceptable than ABPM. However, these trials were small (sample sizes 87 to 220), not randomized trials, and not conducted in the USA.8,11 Additional methods for measuring BP outside of the clinic or office such as BP “kiosks” found in pharmacies or clinic waiting areas offer another alternative, but the adherence to and acceptability of this method have not been previously studied. The extent to which individuals adhere to the recommended number and frequency of measures is likely linked to the acceptability of different methods to measure BP, and may depend on the BP measurement method.6,7,8,9,12,13 Poor adherence may be a consequence of low acceptability and reduces the value of the measurement method for informing clinical actions.

We report here on the results of a randomized controlled diagnostic study which included a comparison of the acceptability and adherence of clinic, home, kiosk, and ABPM monitoring among adults with elevated BP who had not been diagnosed with hypertension in primary care.

METHODS

The study design and methods for the Blood Pressure Checks for Diagnosing Hypertension trial (BP CHECK) have been reported in full.14,15 This comparative diagnostic accuracy study randomized adults presenting to primary care settings with elevated BP, but who did not have a hypertension diagnosis, to one of three methods for measuring BP: clinic, home, and kiosk. A reference standard ABPM was conducted on all participants. Enrollment occurred between May 11, 2017, and March 4, 2019. Study activities were reviewed and approved by the Kaiser Permanente Washington (KPWA) Human Subjects Review Committee, FWA00002344. Written informed consent was obtained from each participant prior to enrollment.

Participants

Participants were adults aged 18–85 who presented to one of 12 clinics operated by KPWA in Washington State, USA, with elevated BP (≥ 138 mmHg systolic or ≥ 88 mmHg diastolic) in the last 2 years, but who did not have a hypertension diagnosis and no hypertensive medication in the medical record. Potentially eligible individuals were contacted by the research team and invited to an initial screening visit (visit 1). Potential participants who had BP of ≥ 140 mmHg systolic or ≥ 90 mmHg diastolic on each of two measurements by the screening researcher were consented and randomized using a computer-based randomization sequence generator to one of three diagnostic arms. Randomization was stratified by participant’s home clinic, age (< 60 or ≥ 60), and average baseline BP (< 150 or ≥ 150 mmHg systolic).

Study Arms

Participants in the clinic arm were given instructions to attend their own KPWA clinic for a recheck of their BP, following the clinic’s usual procedures for BP measurement. This included usual training of clinical staff in measurement technique and repeat BP if the initial BP is high. Participants in the home arm were given a validated Bluetooth-enabled oscillometric monitor (Omron N786 BP monitor) with a cuff appropriate for their arm size.16 After ensuring the participant was proficient, they were asked to measure their own BP twice after waking up and twice at bedtime for 5 days (total 20 measurements). Participants in the kiosk arm were asked to measure their BP at a validated PharmaSmart BP kiosk at either their home KPWA clinic or a nearby pharmacy.17,18 After ensuring proficiency with using the kiosk, they were asked to measure their BP three times on three separate days (total 9 measurements). Within 3 weeks, each group was given a reminder to complete their tasks. After 3 weeks, individuals returned for a further research visit, during which they were fitted with a validated Welch Allyn 7100 ambulatory BP monitor (ABPM).19 The monitor was to be worn for a 24-h period, during which it measured BP every 30 min from 7 a.m. to 11 p.m. (daytime, total 32 daytime measurements) and every hour from 11 p.m. to 7 a.m. Participants returned the following day at which time the ABPM device was removed.

Outcome Measurement

We measured participant acceptability at three points in the study: visit 1 (baseline 1) prior to randomization; visit 2 (3 weeks after randomization and after completing the assigned diagnostic regimen); and visit 3 (1 day after visit 2 after completing ABPM). Participants completed survey questionnaires at these in-person visits using a computer tablet. At visit 1, participants were asked to answer the survey based on their prior experience of clinic BP measurment. At visit 2, participants were asked to answer the survey based on their study arm: their experience of clinic, home, or kiosk BP diagnostic testing, respectively. At visit 3, participants were asked to answer the survey based on their experience of ABPM diagnostic testing, which they had just completed.

Surveys at each visit included a 13-item acceptability tool which was validated in previous studies of BP measurement and was used to calculate an overall acceptability score.6 Measures also included a 5-item survey on perceptions and beliefs of the accuracy of different methods of BP measurement, and a single question about preference for overall BP measurement. At visits 2 and 3, participants were asked additional questions including 7 items on their BP measurement experience (designed for the study) and 4 items regarding their level of confidence and trust in the BP diagnostic method.11

Adherence was defined based on the number of BP measurements completed between randomization and visit 2. The pre-specified definitions of adherence by randomization arm were as follows: (1) clinic—evidence in the electronic medical record of at least one clinic visit by the participant that included a BP measurement, (2) home—16 or more home BP measurements on 4 different days,20,21 and (3) kiosk—6 or more BP measurements at a kiosk on at least 2 different days.15,18 Adherence to ABPM was defined as at least 14 daytime BP measurements occurring between visit 2 and visit 3.22

Analyses

We calculated the mean (SD) of responses to Likert-scale items from the 13-item acceptability questionnaire.6 Item responses ranged from 1 = strongly agree to 7 = strongly disagree, with item scores reversed where appropriate such that higher scores indicated greater acceptability. A total acceptability score was computed as the mean of the item-level responses. Wilcoxon matched-pair signed rank tests were used to test for within-person differences between acceptability measures for the diagnostic measurement method (clinic, home, or kiosk; acceptability assessed at visit 2) and ABPM (assessed at visit 3). Linear regression models fit with generalized estimating equations were used to estimate differences in mean acceptability by randomization arm, and to assess whether differences in test acceptability varied by participant characteristics (i.e., age, sex, race/ethnicity, baseline SBP).

Descriptive statistics were used to summarize responses to three other instruments (i.e., 5-item perceptions and beliefs about accuracy, 7-item experience, and 4-item confidence and trust). All items used Likert-scale response categories, and the number and proportion of participants selecting one of the top two categories (corresponding to greater levels of acceptability) were reported by randomization arm. For questions related to perceptions and beliefs about measurement accuracy, responses from visit 1 (before any study-related self-measurement was completed) and from visit 3 (after all measurements were complete) are reported. For the single question asking participants to select the BP measurement method that they preferred, responses from baseline (visit 1) and after all measurements were complete (visit 3) are summarized, stratified by randomization group.

Since BP measurement protocols (number of days and measures per day) differed by randomization arm, reporting of adherence was limited to descriptive statistics. The number and proportion of participants meeting the pre-specified definition of adherence (as detailed above) are reported by randomization arm overall, and by subgroups defined by participant characteristics. Modified Poisson regression models were used to estimate the relative risk of adherence comparing the home and kiosk arms to the clinic arm. Clinic was used as the reference group because this is the diagnostic method used most widely in clinical practice.

RESULTS

A total of 9434 patients were invited to participate in the study, of whom 1476 attended a screening visit and 510 were randomized.14 The mean age of study participants was 59 years, 80% were white, and 51% were male, with a mean BP of 150/88 (at the baseline screening visit) based on two measures taken 1 min apart using a validated Omron 907XL monitor23 and a mean BMI of 30.

Acceptability

The overall acceptability score was highest (i.e., most acceptable) for home BP (mean 6.2, SD 0.7) and lowest (least acceptable) for ABPM (mean 5.0, SD 1.0). Scores were intermediate for clinic (5.5, SD 1.1) and kiosk (5.4, SD 1.0) (Table 1). Using within-person comparisons, overall acceptability was significantly higher for all three measurement methods (clinic, home, and kiosk) compared to ABPM, with home having the highest acceptability compared to ABPM (paired difference of 1.15) followed by clinic (paired difference 0.59) and by kiosk (paired difference 0.39) (Table 2). The three individual items from the acceptability scale with the largest difference between intervention-assigned BP measurement (clinic, home, and kiosk arms) and ABPM were “It disturbed sleep” (differences between clinic, home, and kiosk compared to ABPM were 2.96, 2.83, and 2.73 respectively), “I was uncomfortable” (2.61, 2.59, and 1.54 respectively), and “It disturbed home life or everyday activities” (1.30, 2.71, and 1.33 respectively). While most measures of acceptability favored clinic, home, and kiosk over ABPM, there were a few exceptions. For example, kiosk was rated with significantly lower acceptability scores than ABPM for the items “It made me anxious” (paired difference − 0.99) and “It worried me knowing the blood pressure” (paired difference − 1.13)

Table 1 Acceptability of Blood Pressure (BP) Measurement at the Initial Clinic Visit, in the Three Intervention Arms (Clinic, Home, Kiosk), and for Ambulatory Blood Pressure Measurement (ABPM)
Full size table
Table 2 Within-Group Comparisons Between Acceptability of Clinic, Home, and Kiosk BP, Compared to Ambulatory Blood Pressure Measurement (ABPM)
Full size table

Comparing total acceptability scores across randomization groups, there were no differences between clinic BP and kiosk BP; however, mean acceptability was 0.72 (95% confidence interval 0.51–0.93) greater for home versus clinic. These results were consistent across subgroups defined by participant characteristics (Appendix 2).

Responses to the 7-item instrument regarding experience of BP measurement indicated that kiosk appeared to provide the lowest privacy and was most embarrassing, but provided BP readings that were easiest to understand and gave immediate feedback to users (Appendix 3). Home was the most convenient and easiest to do. Responses to the 4-item confidence instrument demonstrated that particpants had the highest confidence that home measurements produced results that most closely represented their true BP, followed by ABPM, clinic, and kiosk. Participants also expressed confidence home was the most likely to be successful in determining if they truly had hypertension (Appendix 4).

Adherence

Adherence to the minimum number of BP readings pre-specified in the study protocol was higher for home (154/170, 90.6%) and clinic (150/172, 87.2%) than for kiosk (114/168, 67.9%) (Table 3). For ABPM, 467 of the 510 participants (91.6%) completed at least 14 daytime readings and were not significantly different (p = 0.19) across the 3 arms. Overall, adherence was significantly lower for kiosk compared to clinic (RR 0.78, 95% CI 0.69–0.88), and this difference was consistent across subgroups of participant characteristics (age, sex, baseline SBP, BMI, race) (Appendix 5). In all three groups, the adherence to ABPM was higher than the adherence to their diagnostic assignment, but the difference was statistically significant only in the kiosk group (p < 0.01).

Table 3 Adherence to Clinic, Home, Kiosk, and Ambulatory Blood Pressure Measurement
Full size table

Measurement Method Preferences and Perceptions About Accuracy

Participants’ preferred methods for BP measurement were similar before and after completing study measures for those in the clinic and kiosk groups (Fig. 1), but the proportion of participants in the home group that reported home BP as their preference increased substantially (from 52.4% before to 77.9% after). Participants’ perceptions about accuracy of home BP increased from baseline to visit 3 in all randomization groups (including those who had been randomized to the clinic and kiosk arms) (Appendix 6). In contrast, while the proportion reporting kiosk BP as accurate increased in the kiosk group, there was little change in the home and clinic arms. Perceived accuracy of ABPM increased in each group after experiencing this measure (Appendix 6).

Figure 1
figure 1

Participant preferences for blood pressure measurement by randomization group (clinic, home, kiosk) before (a) and after (b) completing study measures. ABPM, ambulatory blood pressure measurement monitoring; BP, blood pressure; EHR, electronic health record.

Full size image

DISCUSSION

Main Findings

Balancing accuracy of a diagnostic test with other test attributes or patient-centered outcomes is increasingly recognized as essential for providing patients and their clinicians with information needed to make informed choices. Determining the most acceptable method to measure BP for individuals with the highest need is essential, if progress is to be made with better identifying and controlling hypertension in primary care. Based on the results of our trial, home BP measurement is the most acceptable method to individuals with elevated BP who did not yet have a diagnosis of hypertension, followed by measurement in the clinic or at stand-alone kiosks. All three of these methods were more acceptable than ABPM, which appears to be associated with more discomfort and disturbance to sleep and to everyday activities than other methods. These findings were similar across participant subgroups.

Adherence was higher for home (90.6%) and clinic (87.2%) than for kiosk (67.2%). However, the criteria used to define adherence varied between these measures. Adherence to ABPM was high across each of the three arms, with an overall 91.6% completing at least 14 daytime readings, despite being associated with more discomfort and disturbance than other methods. This illustrates the considerations that patients go through with weighing the advantages and disadvantages of diagnostic tests.24

Comparison with Existing Literature

The findings from our trial are largely consistent with those from non-randomized studies that have evaluated the acceptability of different methods of BP measurement; however, our study is not only the first to compare BP kiosks, but also the first to sequentially compare clinic, home, and ABPM measurement while participating in a randomized diagnostic trial using the same validated survey instrument.6,25,26 The preference of home BP over ABPM has been demonstrated from smaller studies from the UK6,8,9 and Greece.7,10 Our results are also consistent with studies that have found higher acceptability of office (clinic) BP than ABPM.7 Commonly cited patient concerns found in previous studies of ABPM are consistent with those noted by participants in our study, including discomfort and disturbance with sleep and daily activities.6,26

Strengths and Limitations

Our trial had several strengths. We compared BP measurement methods using validated BP devices that are in common use and/or recommended widely in the USA. Allocation of individuals to study arms was randomized, minimizing risk of bias due to baseline differences in participants. High rates of adherence with ABPM measurement as the reference standard occurred in all three arms, and only small reductions in survey completion rates between first and third study visits. In addition to measurement of adherence, we used validated instruments used in other studies of BP acceptability.6

We recognize several potential limitations. First, generalizability of our findings may be limited due to recruitment from a single integrated health system of fully insured individuals who not only differ from the distribution of race and ethnicity in the USA as a whole, but who also volunteered to participate in a trial. Second, the prevalence of hypertension among trial participants was higher than that among overall primary care populations, but we specifically recruited individuals with elevated clinic BPs who did not yet have a diagnosis of hypertension. While acceptability and adherence for this population may differ from individuals with lower risk of hypertension (e.g., screening populations) or those using BP to titrate response to therapy (i.e., treated populations), we believe that our results likely apply to these individuals also. Third, our calculated rates of adherence to the different measurement methods depended on the pre-specified minimum numbers and frequency based on previous evidence, yet we acknowledge that these are somewhat arbitrary. In addition, some participants in the clinic arm could have attended their clinic and had a BP measured during healthcare encounters for concerns unrelated to suspected hypertension; therefore, the high rates of adherence to clinic arm may reflect these “incidental” measurements. Finally, we were not able to compare all possible technologies used to measure BP in primary care, such as the acceptability of devices which automatically measure several BP readings in patients in clinic settings, and generate averaged readings.27

Implications for Patients, Clinicians, Researchers, Policy Makers

The accuracy of a test cannot be considered without also knowing other test attributes, such as impact on the individual being tested.28 A systematic review conducted to inform the USPSTF guidance on screening for hypertension indicated that home BP and ABPM were more predictive of cardiovascular events and death than clinic BPs.29 Additionally, the USPTF found major limitations in using clinic-based BP measurements to diagnose hypertension, with pooled estimates demonstrating that hypertension was often missed at screening visits (sensitivity 54%; 95% CI 37–70), and overdiagnosed at clinic follow-up visits for high BP (specificity 55%, 95% CI 42–66).30 Additionally, as we previously reported for this trial, compared to daytime ABPM, mean systolic and diastolic BP was significantly lower for clinic, significantly higher for kiosk, and without significant differences for home (clinic − 4.7 mmHg [95% CI − 7.3, − 2.2]; kiosk 9.5 mmHg [7.5, 11.6]; and home − 0.1 mmHg [− 1.6, 1.5]).14 Given the additional evidence we present that home BP seems to be more acceptable and more trusted by patients than kiosk BP, clinic BP, or ABPM, we recommend that home BP should be considered as a preferred option for patients, clinicians, and health care systems who wish to implement patient-centered diagnosis of elevated BP. Health payors are increasingly reimbursing the costs of home BP monitors for patients, and reimbursement for remote patient monitoring has increased recently, partly as a result of the COVID-19 pandemic and the acceptance of home BP measures as part of HEDIS measures.31

Our findings provide key insights into patient acceptance, preferences, and adherence to four different BP measurement techniques in the context of hypertension diagnosis, showing home BP measurement to have a strong acceptability and adherence. These findings are another factor that should be considered when developing clinical guidelines and standard practices in addition to data on accuracy.