Uneven Accuracy of Home Blood Pressure Measurement: A Multicentric Survey

Abstract

Home blood pressure monitoring (HBPM) is increasingly commonly performed, but the concordance between patient HBPM measurement technique and prevailing recommendations has not been well‐assessed according to the literature. The authors performed a multicentric survey to evaluate the degree of patients' adherence to current recommendations on HBPM, and investigate potential predictors of a higher‐quality self‐measurement. A structured questionnaire was administered to 725 Italian outpatient hypertensive patients (mean age, 52.2±14.4 years). Overall, ≥10 recommended procedures were followed by 52.8% of the participants; only 1.0% followed all recommendations. A total of 49.7% of participants rested for ≥5 minutes before the measurement, 36.8% recorded BP more than once in each measurement session, and 34.3% used a chair or bed saddle to support their back. Less than 40% of the patients received some form of training by health professionals. After multivariate analysis, patients receiving/reading instructions showed higher‐quality HBPM (P<.01). The accuracy of HBPM needs to be improved, and more efforts should be devoted to provide patient training on HBPM, especially on the less‐frequently followed recommendations.

Hypertension diagnosis and control depend on the accurate measurement of blood pressure (BP).1 Office BP monitoring (OBPM) is commonly performed by a variety of clinicians (including doctors, nurses, advanced registered nurse practitioners, physician assistants, and medical technicians), and self‐monitoring of BP by patients at home (HBPM) is becoming increasingly common.2, 3 In fact, HBPM is recommended by current guidelines for the management of hypertension1, 4, 5, 6, 7 because it may decrease the white‐coat effect,8 improve patients' compliance to antihypertensive therapy,9 be more reliable than OBPM,4, 10, 11, 12, 13 and reduce the number of visits14 and costs associated with OBPM.6, 15 Moreover, some studies have shown that even health professionals often do not follow recommendations for BP measurement, which would be anticipated to result in spurious BP readings, potentially leading to mismanagement.16, 17, 18, 19

Like traditional BP measurement, HBPM should also be accurate and performed according to existing guidelines.6, 7, 19, 20, 21 Several authors have highlighted the possible pitfalls that occur during self‐measurement7, 14, 22 and investigated the reliability of different BP‐measuring devices.23, 24 However, the literature on patients' adherence to HBPM recommendations is limited to three surveys performed in one Danish hospital of a total of 355 patients.19, 25, 26 In addition, no study has investigated the potential predictors of inaccurate HBPM, which may be crucial to identify proper solutions.

We carried out a multicentric cross‐sectional survey to evaluate the degree of adherence to current recommendations on HBPM and investigate potential predictors of higher‐quality HBPM.

Methods

From April to June 2013, we asked for participation from all patients with a medical diagnosis of hypertension presenting for ambulatory visits in three Italian public hospitals (Ancona, Ascoli Piceno, Chieti). Eligible patients were older than 18 years, received a recommendation to perform HBPM by a general practitioner or a specialist, had no cognitive disease, and provided written informed consent. The study protocol was approved by the ethics committee of the coordinating center in Chieti. Each participant was asked to perform a self‐measurement, and the procedure was observed by a nurse. The nurse was previously trained to record the level of adherence to current guidelines on HBPM using a structured questionnaire (reported as online supplementary content, Data S1).

The questionnaire included 15 items, which were designed to evaluate whether the patient followed 15 specific recommendations included in current Italian guidelines on HBPM.21 The questionnaire also included a few items collecting information on the hospital unit, eventual instructions received by the patient, type of device typically used for self‐measurement, and patients' age, sex, marital status, and education level.

To derive a proxy of the overall adherence to HBPM guidelines, we created a global quality score summing up the answers to each of the 15 items. We assigned one point for each positive answer (adherence met) and zero points for each negative answer (adherence not met). Higher scores indicated higher adherence to guidelines: the maximum possible value (15) meant that during HBPM, patients followed all the recommended procedures.

We evaluated the potential predictors of the level of adherence to guidelines using random‐effect linear regression using the center as the cluster variable. All covariates were included in the model a priori. Multicollinearity, interactions, and higher‐power terms were tested for all covariates. Because the number of missing data was very small (n=4), no missing imputation technique was adopted.

Statistical significance was defined as a two‐sided P value <.05, and all analyses were performed using Stata 11.1 (Stata Corp, College Station, TX).

Results

Characteristics of the Sample and Procedures

Participation was asked to 771 eligible hypertensive patients and obtained from 725 patients. The mean age of the sample was 52.2±14.4 years, 49.5% were men, 12.7% had diabetes, and 29.4% had a diagnosis of dyslipidemia. A total of 97.1% of the participants were treated with antihypertensive medications for 11.3 years on average: 45.9% were using angiotensin‐converting enzyme inhibitors, 42.3% β‐blockers, 41.0% calcium channel blockers, 30.0% diuretics, and 9.0% α‐blockers (Table 1).

Table 1.

Overall Characteristics of the Study Sample

Variables	Overall Sample (N=725)
Male sex, %	49.5
Age, mean (SD), y	52.2 (14.4)
Married, %	74.4
Living status, %
Alone	13.8
In a family	85.1
With a caregiver	1.1
Education level, %
None/elementary	21.9
Middle/high school	60.0
Bachelor/higher	18.1
Systolic blood pressure, mean (SD), mm Hg a	139.0 (14.5)
Diastolic blood pressure, mean (SD), mm Hg a	78.0 (7.9)
Duration of hypertensive treatment, mean (SD) ,y	11.3 (8.1)
Antihypertensive therapy
ACE inhibitors or ARBs, %	45.9
β‐Blockers, %	42.3
Calcium channel blockers, %	41.0
Diuretics, %	30.8
α‐Blockers, %	9.0
Drugs, mean (SD), No.	1.7 (0.7)
Cardiovascular risk factors, %
Current smoking	7.6
Former smoking	16.3
Diabetes	12.7
Dyslipidemia	29.4
Center, %
Chieti‐Pescara	28.6
Ascoli Piceno	57.2
Ancona	14.2

Abbreviations: ACE, angiotensin‐converting enzyme; ARB, angiotensin receptor blocker; SD, standard deviation. ^aMeasured by a nurse after the assessment.

More than half of the patients received either no instructions at all on how to perform HBPM (28.8%) or read the instructions by themselves (25.0%; Table 2). When the patient was trained, most commonly it was by a physician (24.0%). More than 60% of patients measured their BP occasionally, without following a fixed schedule. The most frequent devices used for HBPM were electronic, automatic (50.8%), and semiautomatic (24.7%).

Table 2.

Characteristics of Blood Pressure Self‐Measurement

Blood Pressure Self‐Measurement	Overall Sample
	(N=725), %
Instructions, written or verbal, on the correct use of blood pressure device and the measurement procedure
I received no instructions at all	28.8
I read the instructions by myself	25.0
I received instructions by friends	6.4
I received instructions by a pharmacist	5.0
I received instructions by a nurse	10.8
I received instructions by a doctor	24.0
How many BP measurements do you routinely perform?
Occasionally, I do not follow a fixed schedule	63.1
About 1 per week	15.3
About 2 per week	7.9
About 1 per day	6.9
About 2 per day or more	6.8
Type of device to measure BP, %
Mercurial	12.1
Aneroid	0.3
Electronic, automatic	50.8
Electronic, semiautomatic	24.7
Electronic, manual	5.9
Electronic, wrist	6.2

Adherence to HBPM Guidelines

Of the 15 recommended practices, 10 were followed by more than 60% of patients. Five recommendations, however, were followed by less than half. In particular, 32.4% of the participants performed HBPM at the same hour; 36.8% recorded BP more than once in each measurement session; 27.4% kept a diary; 34.3% used a chair or bed saddle to support their back during the procedure; and 49.7% rested for ≥5 minutes before the measurement. Overall, eight or more of the 15 procedures were followed by 80.3% of the participants; ≥10 by 52.8%; ≥12 by 17.0%, and only 1.0% followed all of the 15 recommended practices (Table 3).

Table 3.

Adherence to Guidelines for the Self‐Measurement of Blood Pressure in the Study Sample (N=725)

Items a	Yes, %	95% CI
1a. Do you always measure blood pressure at the same hour (ie, always fasting in the morning or after eating in the evening)? a	32.4	28.9–35.8
1b. If not, at what hour do you measure blood pressure more frequently? a
Before breakfast	13.6	10.6–17.1
After breakfast	30.1	25.9–34.6
Before lunch	22.6	18.9–26.8
After lunch	17.8	14.4–21.6
Before dinner	11.9	9.0–15.2
After dinner	4.0	2.4–6.2
2. Do you always measure blood pressure using the same arm? a	71.4	68.1–74.7
3a. Do you always measure blood pressure in the same body position (ie, always sitting or lying)? a	94.1	92.3–95.8
3b. If so, in which body position do you usually measure blood pressure? a
Sitting on a chair	87.1	84.3–89.5
Sitting on the bed	5.4	3.8–7.4
Lying	6.7	5.0–8.9
Standing up	0.7	0.2–1.7
4. Do you repeat the measurement after some minutes (then take the mean of the two measurements)?	36.8	33.3–40.3
5. Do you keep a diary of blood pressure measurements? a	27.4	24.1–30.6
6. Did the patient choose the cuff on the basis of his arm circumference?	77.6	74.6–80.7
7. Did the patient put the cuff on properly?	62.8	59.2–66.3
8. Before blood pressure measurement, did the patient rest for at least 5 minutes?	49.7	46.0–53.3
9. During blood pressure measurement, was the room calm, with low noise and no distractions (eg, people talking, radio/television on)?	71.6	68.3–74.9
10. During blood pressure measurement, was the patient silent?	63.7	60.2–67.2
11. During blood pressure measurement, did the patient keep his legs uncrossed?	90.1	87.9–92.3
12. During blood pressure measurement, was the patient's back supported by a chair or bed saddle?	34.3	30.9–37.8
13. During blood pressure measurement, was the patient's arm supported (ie, on a table if sitting or on a bed if outstretched)?	85.4	82.8–88.0
14. During blood pressure measurement, was the patient's arm positioned at the same height of the heart?	78.8	75.8–81.7
15. During blood pressure measurement, was the point where the bladder arm was located uncovered?	65.2	61.8–68.7
Overall pattern
Eight or more positive answers to the above questions b	80.3	77.4–83.2
Ten or more positive answers to the above questions b	52.8	49.2–56.5
Twelve or more positive answers to the above questions b	17.0	14.2–19.7
All (N=15) positive answers to the above questions b	1.0	0.3–1.7

^aDirectly reported by the patients. ^bExcept questions 1b and 3b.

Predictors of Higher‐Quality HBPM

At multivariate analysis, the only variable that was independently associated with the level of adherence to guidelines on HBPM was the source of instructions on the procedure. As compared with patients who received no instructions at all, those who received information by doctors and pharmacists and who read the instructions by themselves were significantly more likely to conduct a higher‐quality HBPM (all P<.01). No significant improvement was observed when the instructions were provided by a nurse (Table 4).

Table 4.

Random‐Effect Linear Regression Predicting Higher‐Quality BP Self‐Measurement

Variables	Higher‐Quality BP Self‐Measurement
	Crude Coefficient (95% CI)	Adjusted Coefficient (95% CI) a	P Value a
Male sex	0.19 (−0.14; 0.52)	0.23 (−0.09; 0.55)	.17
Married	0.38 (0.00; 0.75)	0.27 (−0.22; 0.75)	.2
Age, 1‐y increase	0.02 (0.00; 0.03)	0.01 (0.00; 0.02)	.15
Living in a family or with a caregiver	0.09 (−0.39; 0.57)	−0.03 (−0.57; 0.51)	.9
Current cigarette smoking	0.82 (−0.76; 2.40)	0.92 (−0.95; 2.74)	.3
Diabetes	−0.59 (−1.85; 0.68)	−0.77 (−2.10; 0.56)	.3
Dyslipidemia	0.17 (−0.69; 1.04)	0.13 (−0.81; 1.07)	.8
Education level
None/elementary	1	1	–
Middle/high school	−0.41 (−0.75; −0.08)	−0.06 (−0.51; 0.38)	.7
Bachelor/higher	0.50 (0.08; 0.93)	0.55 (−0.06; 1.16)	.08
Systolic BP, 1‐mm Hg increase	0.01 (−0.02; 0.04)	0.01 (−0.02; 0.04)	.4
Years of hypertension	0.03 (−0.03; −0.08)	0.02 (−0.05; 0.08)	.6
Hypertension treatment
ACE inhibitors	0.97 (−0.24; 2.17)	0.93 (−0.35; 2.22)	.15
β‐Blockers	−0.45 (−1.31; 0.41)	−0.43 (−1.33; 0.47)	.3
Calcium channel blockers	0.03 (−0.84; 0.90)	0.06 (−0.89; 1.01)	.9
Diuretics	0.36 (−0.57; 1.29)	0.25 (−0.79; 1.30)	.6
α‐Blockers	−0.86 (−2.34; 0.62)	−0.81 (−2.39; 0.76)	.3
Number of drugs, 1‐unit increase	0.02 (−0.41; 0.45)	0.01 (−0.45; 0.47)	.9
Instructions on the correct use of BP device
I received no instructions at all	1	1	–
I read the instructions by myself	0.13 (−0.25; 0.51)	0.68 (0.24; 1.13)	.003
I received instructions by friends	−0.09 (−0.77; 0.59)	0.53 (−0.19; 1.25)	.15
I received instructions by a pharmacist	1.20 (0.45; 1.95)	1.67 (0.88; 2.47)	<.001
I received instructions by a nurse	−0.13 (−0.66; 0.40)	0.48 (−0.11; 1.07)	0.11
I received instructions by a doctor	0.70 (0.32; 1.08)	1.09 (0.64; 1.54)	<.001

Abbreviations: ACE, angiotensin‐converting enzyme; BP, blood pressure; CI, confidence interval. ^aRandom‐effect linear regression model using the center as the cluster unit.

Discussion

In Northern Italy,27 as well as in other Western countries,28, 29 it has been estimated that most outpatient hypertensive patients––up to 75%––are regularly performing HBPM. However, only three Danish assessments of the appropriateness of HBPM are available so far.19, 25, 26

In this sample of hypertensive patients, the level of adherence to current guidelines on HBPM was not consistent: some of the recommended practices for HBPM were followed by a large proportion of patients (use of the same arm and body position, proper choice of cuff, silent room and patient, correct arm and body position, use of arm supports, no clothes over cuff), whereas patients' compliance to other recommendations was unacceptably low. In particular, <40% of the patients performed HBPM at the same hour, used a chair or bed saddle to support their back during HBPM, and repeated the procedure after some minutes, and only half rested for ≥5 minutes before the measurement. Importantly, while it may at first glance appear reassuring that a majority of persons performed more than half of the appropriate steps in HPBM, any single critical step in HBPM can result in spurious readings that mislead proper management.

Previous findings were slightly more negative. The only three recent Danish surveys that were specifically focused on this topic reported an even lower quality of HBPM: none of the hypertensive participants and pregnant women followed all recommended practices,19 and <10% adhered to the required 5‐minute rest time before taking the first measurement.25, 26 Notably, in a previous survey with similar methodology, we found that the overall compliance to guidelines of the BP measurement made by health professionals was substantially lower than HBPM (≥10 recommendations were followed in 33.4% vs 52.8% of the measurements).16 Although this is just an indirect comparison, a similar superiority of HBPM over OBPM was reported by most randomized head‐to‐head comparisons.30, 31, 32, 33, 34

The most likely explanation of such a low adherence to some of the recommended practices for HBPM is scarce training received by the patients.35 In 2010, a Canadian study reported that less than one third of the patients routinely using HBPM were given specific training on proper measurement techniques, and having received instructions from a health care professional was the strongest factor associated with a correct HBPM.36 Our survey confirms such findings: <40% of the participants received some form of training by a health professional, and when patients were instructed, the quality of HBPM significantly improved. Importantly, even the patients who read the instructions alone showed a significantly higher adherence than those who received no instructions at all, reinforcing the pivotal importance of accurate patient training.

Interestingly, the impact of instructions on the patients seemed to vary depending on who gave the information. The probability of a higher‐quality HBPM was significantly increased when doctors or pharmacists provided the instructions; conversely, no improvement was observed when instructions were given by nurses. The latter finding on nurse role is novel and should be considered preliminary. If confirmed, however, it deserves attention, suggesting that either the quality/quantity of the instructions provided by the nurses are suboptimal or that patients pay less attention to nurses' than doctors' advice, or both.

Such a suboptimal communication between health professionals and patients might be among the reasons for the surprisingly low percentage of patients declaring they have received some form of training. Given that current guidelines recommend accurate training as an essential prerequisite for high‐quality HBPM,4, 6, 21 it could be hypothesized that some of these patients actually received instructions but did not pay enough attention to them. Whether such a lack of training was caused by poor communication or scarce adherence to guidelines, more attention must be paid to this issue.

Given that the quality of HBPM is influenced by the accuracy and completeness of the instructions provided, efforts should be made to raise awareness among health professionals on the importance of patient training, with a special emphasis on the recommendations that are less frequently followed and are more important for a reliable measurement. First and foremost, patients should be informed of the importance of performing the measurement more than once, given that recent studies observed a difference in systolic BP of ≥10 mm Hg across temporarily close measurements in 30% of patients,37 and a 40% probability of misdiagnosis with a single measurement.38 Second, operators should educate patients to always measure their BP at the same time to avoid the misdiagnosis caused by the well‐known circadian variations of BP,39 which are even more pronounced among hypertensive patients.40 Third, patients should be instructed on the importance of a correct body position while performing BP measurement. Indeed, previous literature suggests that taking BP with the back unsupported may falsely elevate pressure levels by 6 mm Hg to 10 mm Hg41 and that crossing the legs may increase systolic BP by 2 mm Hg to 8 mm Hg.42 Finally, patients should be made aware of the risk of overestimating their BP up to 10 mm Hg when BP is measured without resting before the procedure.43

Study Limitations

This study has some limitations that must be considered. First, because of the cross‐sectional design of the survey, we could not determine causal relationships but only associations in the analysis of the predictors of HBPM quality. Second, although our sample consisted of patients from three large public reference hospitals, we were not able to enroll patients from private clinics, and the sample was not derived using a randomized multistage sampling technique. Thus, the sample cannot be considered representative of the overall population of Italian hypertensive patients. Third, despite the multivariate analysis accounting for the cluster effect of the hospital, we considered only a limited number of select predictors of quality, and several others including the duration of HBPM might be present. Fourth, despite the nurses being recommended to be as unobtrusive as possible while observing patients during self‐measurement, it is likely that some participants changed their behavior, measuring their BP with more accuracy than at home. Thus, the overall level of HBPM quality is likely to be overestimated.

Conclusions

In this sample of hypertensive patients, the accuracy of HBPM needs to be improved. Several of the recommended procedures were followed by most patients, but the level of adherence to other important recommendations was unacceptably low. HBPM quality significantly improved when doctors or pharmacists provided instructions to patients, but most patients received no instructions by health operators. More effort should be devoted to provide accurate patient training on HBPM procedures, with particular attention to the recommendations that are less frequently followed.

Disclosures

The authors report no specific funding in relation to this research and no conflicts of interest to disclose.

Supporting information

Data S1. Questionnaire administered to the sample of hypertensive patients (translated from Italian).

J Clin Hypertens (Greenwich). 2015;17:638–643. DOI: 10.1111/jch.12552. © 2015 Wiley Periodicals, Inc.