High Prevalence of Hypertension in a Danish Population Telemedical Home Measurement of Blood Pressure in Citizens Aged 55–64 Years in Holstebro County

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Original article

Hypertension is the most prevalent chronic condition in the population. It is estimated that 10% of the health care spending are directly related to hypertension and its compli- cations.¹ Reduction of blood pressure (BP) in hypertensive patients reduces morbidity and mortality.² The World Health Organization has made it a goal to reduce hypertension by 25% by the year of 2025.³

When only measuring BP in the office (OBP), we overlook patients who could benefit from antihypertensive treatment because their home BP (HBP) is elevated (masked hypertension, MH). In addition, patients with elevated OBP may receive nonbeneficial treatment in spite of normal HBP (white coat hypertension, WCH).

HBP measurements are not influenced by the clinic set- tings and thus have a higher diagnostic accuracy.^4,5 The method is cost-effective and patients seem to prefer it instead of 24-hour ambulatory BP measurements.^6,7 HBP is

prognostically superior to OBP and similar to ambulatory BP.^5,8,9 Recent guidelines recommend the use of HBP measurements for the diagnosis and treatment of hypertension.^10,11 The aim of this study was to determine the prevalence of hypertension among citizens of Holstebro, Denmark, aged 55–64 years, including the well treated, the untreated, and the insufficiently treated, and to estimate the prevalence of WCH and MH using HBP with telemedical data transmission.

METHODS Patients

This study was designed as a population study in the municipality of Holstebro, which has approximately 57,000 inhabitants. Inclusion criteria were age 55 to 64 years, registered address in the municipality, and enrollment at a practice

High Prevalence of Hypertension in a Danish Population Telemedical Home Measurement of Blood Pressure in Citizens Aged 55–64 Years in Holstebro County

Nikolai Hoffmann-Petersen,

¹

Torsten Lauritzen,

²

Jesper Nørgaard Bech,

¹

and Erling Bjerregaard Pedersen

¹

BACKGROUND

Home blood pressure (HBP) is prognostically superior to office BP (OBP) and similar to ambulatory BP measurements. We determined the prevalence of hypertension using HBP with telemedical data transmission in the municipality of Holstebro, Denmark (57,000 citizens).

METHODS

Using the Civil Registration System, we invited citizens aged 55–64 years to have their OBP and HBP measured using telemedical data transmission. Elevated OBP was defined as ≥140/90 mm Hg. HBP was measured 3 times daily on 3 consecutive days with 3 measurements on each occa- sion. HBP was the mean of all measurements on day 1 and 3, and hypertension was defined as ≥135/85 mm Hg.

RESULTS

We included 3,102 citizens who had performed at least 12 HBP measurements during day 2 and 3. Group 1: (n = 1,464, 47%) had both normal OBP and HBP. Group 2: (n = 838, 27%) had both elevated OBP and HBP indicating persistent hypertension. Group 3: (n = 560, 18%) had

elevated OBP and normal HBP indicating white coat hypertension (WCH). Group 4: (n = 240, 8%) had normal OBP and elevated HBP indicating masked hypertension (MH). Thus, 1,078 (35%, groups 2 and 4) were untreated or insufficiently treated. Awareness of hypertension was registered in 950 patients (31%) and of these 49% had a normal HBP.

CONCLUSIONS

This is the first large-scale study to eliminate completely reporting bias by using telemedical transmission of BP data. One third of citizens in the age group 55–64 years had an abnormally high HBP, and one fourth either had WCH or MH.

clinicaltrialsregistration

ClinicalTrials.gov identification number: NCT02355392

Keywords: control; home blood pressure; hypertension; MH; prevalence;

telemedical home blood pressure; telemedicine; treatment; WCH.

doi:10.1093/ajh/hpv116

Correspondence: Nikolai Hoffmann-Petersen (nikhof@rm.dk).

Initially submitted February 17, 2015; date of first revision March 3, 2015; accepted for publication June 30, 2015.

For Permissions, please email: journals.permissions@oup.com

1University Clinic of Nephrology and Hypertension, Department of Medical Research and Medicine, Holstebro Hospital and Aarhus University, Holstebro, Denmark; ²Department of Public Health, Section of General Practice, Aarhus University, Aarhus, Denmark.

at Aarhus Universitet / Statsbiblioteket on August 4, 2015http://ajh.oxfordjournals.org/Downloaded from

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of one of the general practitioners (GPs) who had agreed to participate in the study. Exclusion criteria were unwilling- ness to participate or incapability to do HBP measurements.

Procedure

The citizens and GPs of Holstebro were invited. Names and addresses were drawn from the Civil Registration System of Central Region Denmark that contains information on the GP, whom the citizens attended at the time of the drawing. All patients registered with 1 particular practice were drawn at a time. In this way, the drawings were from an actual dynamic population aged 55–64 years during the whole time of recruitment.¹² The patients were sent an invitation letter, and when necessary a reminder was sent. Appointments for further information were done through telephone or e-mail. Participants who changed registration with a GP were only invited once. The municipal preventive care center managed all equipment logistics.

In the office (municipality care center), the BP was measured 3 times after 5 minutes of seated rest.¹¹ The mean value of the measurements was calculated as OBP. Instructions were given about the use of the telemedical HBP measurement equipment. A personal medical history and use of medication were obtained by means of a questionnaire. This comprised 9 ques- tions: Are you diagnosed with hypertension? Are you diagnosed with diabetes? Are you diagnosed with kidney disease (in case of a yes, which type)? Are you diagnosed with ischemic heart disease? Have you had a stroke? Do you smoke (in case of a yes, how much)? Do you drink alcohol (in case of a yes, how much)?

How many hours weekly do you do exercise (e.g. walking, walk on stairs, cleaning, and gardening)? Do you take medicines?

The participants were asked to do 3 BP measurements at home with an interval of 1 minute, in the morning before breakfast and drug intake if treated, 3 measurements before supper and 3 measurements before going to bed. The HBP was calculated as the average of all the measures on days 2 and 3. A valid HBP had 12 or more measures on days 2 and 3. After 3 days, the participants returned the equipment.

Classification of hypertension

In the present study we have analyzed the BP values according to the most recent European Society of Hypertension/

European Society of Cardiology guideline.¹¹ An elevated OBP was defined as ≥140/90 mm Hg. An elevated HBP was defined as ≥135/85 mm Hg. In the subanalysis of diabetic patients, definition of elevated OBP was ≥140/85 mm Hg and elevated HBP ≥135/80 mm Hg.

Controlled hypertensives were patients known with hypertension (self-reported) and a HBP below the limits.

Uncontrolled hypertensives were patients known with hyper- tension, but with HBP above the limits.

Devices

In the first part of the study, we used A&D 767PlusBT (A&D Company Limited, Tokyo, Japan) BP monitors¹³ for both OBP and HBP measurements (n = 1,579). We used A&D cuffs, sizes depending on the patient’s upper arm. Data were sent using a Tunstall RTX3371 telehealth monitor Tunstall Healthcare A/S,

Noerresundby, Denmark), with Global System for Mobile communication/General Packet Radio Service communication to a central server. A summery report was extracted from the Tunstall Triagemanager software and 1 copy was given to the patient and another sent to the patients’ GP. In the second part, we used Omron 705IT (Omron Healthcare, Kyoto, Japan) BP monitors¹⁴ for the both OBP and HBP measurements (n = 1,523).

We used Omron cuffs, sizes depending on the patient’s upper arm. Data were sent using a Numera (Numera, Seattle, WA) telehealth monitor with Global System for Mobile communication/General Packet Radio Service communication to a central server. The mean of HBP measurements was sent to the GP’s electronic patient record using the Danish MedCom standard.

A summary was extracted from the Columna Citizen Platform (Systematic A/S, Aarhus, Denmark) and given to the patient.

Ethics

All participants were given oral and written information about the project. All gave written consent. The study was approved by the Scientific Ethical Committee of Central Region Denmark (j.no.:M-2011011) and by the Danish Data Protection Agency (j.no.:2011-41-5703).

Statistics

Continuous variables are reported as means with SDs and categorical variables as percentages. Student’s t-tests were used for comparison of unpaired continuous variables.

Pearson’s chi-squared tests were used for comparison of categorical variables. A 2-tailed P-value <0.05 was considered significant. Statistical analyses were performed using the SPSS version 20 (IBM, Armonk, NY).

RESULTS Demographics

In the municipality of Holstebro, the 40 GPs are organized in 18 different offices. All but 1 practice (2 GPs) agreed on participating in the study. From the 17 practices, we invited all citizens in the aged 55–64 years, i.e. 6,405 citizens, ending up with 3,159 (49%) attendees and 3,246 (51%) nonattendees (Figure 1). Of 3,159 participants, 3,102 did sufficient HBP measurements that were used for further analysis. Mean age was 60 years. Clinical data are shown in Table 1. Mean body mass index was 27 kg/m² and thus in the middle of the defined overweight status ranging from 25 to 30 kg/m². Smokers accounted for 17% (n = 512) with a mean cigarette consumption of 14 ± 7. Median alcohol consumption per week was 4.5 units (=72 g of alcohol).

Prevalence of hypertension

Sufficient measurements of HBP and OBP were done in 3,102 individuals. Normal OBP and HBP were found in 47% as shown in Table 2. Elevated OBP and HBP in 27%

(n = 838) and WCH in 18% (n = 560). MH was diagnosed in 8% (n = 240). The same prevalences of normotension, WCH, and MH were found for each of the 2 BP monitors used in the study (Table 2). According to the questionnaire, 31%

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(n = 950) of patients had diagnosed hypertension, of these 49% (n = 467) had controlled hypertension. In the group of patients not previously diagnosed with hypertension, 28%

(n = 594) were hypertensive, 18% had WCH and 5% MH.

Likewise, controlled hypertension was only found in 54%

(n = 539) of patients receiving antihypertensive treatment.

Prevalence of hypertension in this age group was 50%

when adding patients previously diagnosed with hypertension (n = 950) to the number of patients found with hypertension in our study (n = 594).

Characteristics of a person with MH or WCH

The last section of Table 2 shows clinical data according to different BP classes: normotension, WCH, MH, and persistent hypertension. Only minor differences are seen between the groups and none of the differences can identify a high- risk profile of individuals having MH or WCH.

Different OBP cutoffs shows different prevalences of MH and WHC (Table 3). Prevalence of MH is gradually decreasing with decreasing cutoff values of OBP. By a cutoff OBP <

125/75, only 0.7% had MH. Likewise, is the prevalence of WCH gradually decreasing with increasing cutoff values of OBP. By a cutoff OBP ≥165/115 only 0.7% had WCH.

Prevalence of hypertension in relation to level of blood pressure

Figure 2 shows the prevalences of individuals who had normotension, WCH, MH, and persistent hypertension.

If the diagnostic threshold of normotension is reduced by

5 mm Hg to an OBP < 135/85 and HBP < 130/80, the prevalence of persistent hypertension will increase from 27%

(n = 838) to 44% (n = 1,363). In contrast, the prevalence of persistent hypertension will decrease to 14% (n = 445) by increasing the threshold of normotension by 5 mm Hg to OBP < 145/95 and HBP < 140/90. If the diagnostic threshold of normotension is reduced by 10 mm Hg to OBP < 130/80 and HBP < 125/85, the prevalence of persistent hypertension will increase from 27% (n = 838) to 64% (n = 1,981). In contrast, the prevalence of persistent hypertension will decrease to 8% (n = 244) by increasing the threshold of normotension by 10 mm Hg to OBP < 150/100 and HBP < 145/95.

Antihypertensive treatment

Table 4 shows antihypertensive therapy in participants with known hypertension subdivided into controlled and uncontrolled hypertension. A significant difference was observed in the number of patients not treated for hypertension, 4%

(n = 17) vs. 11% (n = 52). The mean number of antihypertensive drugs 2.0 ± 1.0 in the group of controlled hypertension differed significantly from the mean 1.6 ± 1.0 in the group of uncontrolled hypertension. More patients with controlled hypertension received thiazid diuretics (52% vs. 42%), spironolactone (3% vs. 1%), beta-blockers (26% vs. 19%) and were diagnosed with ischemic heart disease (12% vs. 7%).

Prevalence of hypertension in patient with diabetes

We registered 165 diabetic patients (5%): 71 females and 94 males. Mean systolic OBP was 136 ± 19 and mean

Figure 1. Flow diagram for the study participants. Abbreviations: OBP, office blood pressure; HBP, home blood pressure. at Aarhus Universitet / Statsbiblioteket on August 4, 2015http://ajh.oxfordjournals.org/Downloaded from

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diastolic OBP was 82 ± 10. Mean systolic HBP was 130 ± 15 and mean diastolic HBP was 78 ± 8. Using OBP ≥140/85 and HBP ≥135/80 as definition of elevated BP among the diabet- ics, we found that 95 (58%) were well controlled.

DISCUSSION

We measured BP using telemedically transmitted HBP in a population aged 55–64 years. One third (35%) of the patients had abnormally high HBP, and one fourth (23%) had either WCH or MH. Only 49% of the patients known with hypertension reached BP goals. Among patients not known with hypertension, 23% were hypertensive, 18% had WCH, and 5% had MH. Prevalence of hypertension in this age group was 50%.

The prevalence of hypertension in Denmark has previously been estimated based on OBP.^15–18 Among 6,784 individuals, aged 30–60 years, 39% had hypertension.¹⁵ Among 5,413 hypertensive patients, aged 20 years and older, 29% had optimally treated hypertension.¹⁷ Using the Danish General Practice Database, 33% of 37,651 patients with hypertension reached treatment target of OBP < 140/90.¹⁸ Among 7,767

individuals, aged 20–89 years, the prevalence of hypertension was 26% based on OBP.¹⁶ HBP were performed in 711 patients, the prevalence of hypertension was 22% based on self-reported measurements.¹⁶ It was estimated that 43%

of hypertensives in Denmark were controlled.¹⁶ But these results have a considerable uncertainty as HBP was only measured in patients screened with elevated OBP. Using HBP, we found that among people aged 55–64 years and with previously known hypertension 49% had controlled hypertension. Thus, only half of the patients aware of their hypertension were sufficiently treated. The mean number of antihypertensive drugs in the group of uncontrolled hypertension was only 1.6 ± 1.0, leaving room for improvement.

Possible factors are doctor’s inertia, patients’ resistance to

“another pill” and fear of adverse reactions.¹⁹

Large variations are seen in the reported prevalence and control of hypertension.^20,21 Hypertension affects about one third of the US population.²⁰ Recently, a population study from the Kaiser Permanente Southern California demon- strated an increase in controlled hypertension from 54%

to 86% from 2004 through 2012.²² In the National Health and Nutrition Examination Survey 2007–2008, BP was

Table 1. Demographics and clinical data

Characteristics Total Female Male

Number of study participants 3,102 1,635 1,466

Age, mean (SD), years 60 (3) 60 (3) 60 (3)

Height, mean (SD), cm 171 (9) 165 (6) 178 (7)

Weight, mean (SD), kg 80 (16) 73 (14) 88 (14)

Body mass index, mean (SD)^a 27 (5) 27 (5) 28 (4)

Waist circumference, mean (SD), cm 96 (13) 91 (13) 102 (11)

OBP, systolic, mean (SD), mm Hg 136 (18) 133 (18) 138 (18)

OBP, diastolic, mean (SD), mm Hg 84 (10) 83 (10) 84 (10)

HBP, systolic, mean (SD), mm Hg 126 (14) 125 (14) 128 (13)

HBP, diastolic, mean (SD), mm Hg 79 (8) 78 (9) 79 (8)

Number of HBP measurements excluding day 1, mean (SD) 18 (3) 18 (3) 18 (3)

Known with hypertension^b, % (n) 31% (950) 30% (491) 31% (459)

OBP, systolic (known with hypertension), mean (SD), mm Hg 140 (19) 138 (19) 142 (18)

OBP, diastolic (known with hypertension), mean (SD), mm Hg 86 (10) 86 (10) 86 (10)

HBP, systolic (known with hypertension), mean (SD), mm Hg 131 (14) 130 (15) 133 (13)

HBP, diastolic (known with hypertension), mean (SD), mm Hg 81 (8) 81 (8) 81 (8)

Diabetes^b 5% (n = 165) 4% (n = 71) 6% (n = 94)

Kidney disease^b 1% (n = 21) 1% (n = 11) 1% (n = 10)

Prior ischemic heart disease^b 5% (n = 147) 3% (n = 51) 7% (n = 96)

Prior stroke^b 3% (n = 86) 2% (n = 34) 4% (n = 52)

Current smoker^b 17% (n = 512) 15% (n = 248) 18% (n = 264)

Tobacco consumption among smokers,^b,c mean (SD) 14 (7) 12 (7) 15 (8)

Alcohol consumption,^b,d,e median 4.5 3 6

Physical exercise,^b,d,f median 14 14 14

Abbreviations: OBP, office blood pressure; HBP, = home blood pressure; n = number of participants.

aCalculated as weight in kilograms divided by height in meters squared. ^bSelf-reported data. ^cNumber of cigarettes per day. ^dData are not normally distributed, reported as medians. ^eAlcohol units per week (1 unit equals 12 g of alcohol). ^fHours of light exercise per week.

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controlled in 50% of all patients with hypertension.²⁰ Despite the apparent benefits and frequent use of HBP measurements, most population surveys are based on OBP measurements. Among patients with awareness of hypertension the National Health and Nutrition Examination Survey 2009–

2010 found that 31.9% were engaged in monthly or more frequent HBP measurements.²³ The Ohasama study (n = 1,174) showed that among treated hypertensives aged 40–64 years 46% had HBP above limits (≥135/85).²⁴ In the Finn-Home study it was found that among 2,051 participants, aged 45–74 years, the prevalence of hypertension in year 2000 was 43% based on HBP.²⁵ Among treated hypertensives in that study, 67% had a HBP above limits. Among treated hypertensives in our study 45% had a HBP above the limits, which is comparable to the findings in the Ohasama study.

In the Hypertension Optimal Treatment substudy compar- ing OBP and HBP among 926 treated hypertensives OBP was 138 ± 15/83 ± 8 mm Hg and HBP 137 ± 14/83 ± 8 mm Hg.²⁶ We found treated hypertensives to have a mean OBP 138 ± 18/85 ± 10 mm Hg and HBP 129 ± 13/80 ± 8 mm Hg on days 2–3. Thus a good agreement in OBP but the higher HBP in the Hypertension Optimal Treatment substudy can partly be explained by inclusion of all HBP measurements whereas we excluded day 1.¹¹ Based on OBP, we found that 51% of treated hypertensives had BPs above threshold. This is much alike the US control rates and far behind the Kaiser Permanente results.²² In 2011, the US Department of Health and Human Services launched an initiative, Million Hearts, aiming to prevent 1 million heart attacks and strokes by 2017.²⁷ Million Hearts has a clinical goal of achieving 70%

Table 2. Prevalence of normotension, WCH, MH, and persistent hypertension. Clinical data according to different blood pressure classes;

normotension, WCH, MH, and persistent hypertension

Normal home blood pressure Elevated home blood pressure

Characteristics Normotension WCH MH

Persistent hypertension OBP < 140/90

HBP < 135/85 OBP ≥ 140/90

HBP < 135/85 OBP < 140/90

HBP ≥ 135/85 OBP ≥ 140/90 HBP ≥ 135/85 All participants

(n = 3,102) 47%

(n = 1,464) 18%

(n = 560) 8%

(n = 240) 27%

(n = 838) All participants, mean OBP

systolic (SD)/diastolic (SD) 123(10)/77(7) 146(10)/89(7) 127(9)/81(7) 154(16)/93(9)

All participants, mean HBP

ystolic (SD)/diastolic (SD) 117(8)/73(6) 124(7)/77(5) 135(9)/85(6) 142(12)/87(7)

A&D 767PlusBT

(n = 1,579) 46%

(n = 733) 19%

(n = 293) 8%

(n = 129) 27%

(n = 424) Omron 705IT

(n = 1,523) 48%

(n = 731) 18%

(n = 267) 7%

(n = 111) 27%

(n = 414) Awareness of hypertension^a

(n = 950) 31%

(n = 291) 19%

n = 176 14%

(n = 129) 37%

(n = 354) No awareness of hypertension^a

(n = 2,151) 55%

(n = 1,173) 18%

(n = 384) 5%

(n = 111) 22%

(n = 483) Blood pressure lowering

treatment^a (n = 990) 36%

(n = 358) 18%

(n = 181) 13%

(n = 130) 32%

(n = 321) No blood pressure lowering

treatment^a (n = 2,109) 52%

(n = 1,106) 18%

(n = 379) 5%

(n = 110) 24%

(n = 514)

Age, years, (SD) 60 (3) 60 (3) 61 (3) 60 (4)

Body mass index, mean (SD)^b 27 (5) 27 (4) 28 (5) 29 (5)

Waist circumference, mean (SD), cm 93 (13) 97 (12) 99 (14) 100 (13)

Gender, male 42% (n = 620) 55% (n = 310) 45% (n = 107) 51% (n = 429)

Diabetes^a 5% (n = 66) 6% (n = 31) 10% (n = 25) 5% (n = 43)

Kidney disease^a .8% (n = 11) .5% (n = 3) 1.7% (n = 4) .4% (n = 3)

Prior ischemic heart disease^a 6% (n = 84) 4% (n = 22) 7% (n = 16) 3% (n = 25)

Prior stroke^a 3% (n = 39) 2% (n = 12) 4% (n = 10) 3% (n = 25)

Current smoker^a 15% (n = 217) 19% (n = 106) 19% (n = 43) 18% (n = 146)

Distribution dependent on whether the study participants reported awareness of hypertension, were receiving blood pressure lowering medication, and which device used for the HBP measurements. Below triple line clinical data are according to the 4 blood pressure classes. Data are reported as percentage (number) of study participants.

Abbreviations: OBP, office blood pressure; HBP, home blood pressure.

aSelf-reported data. ^bCalculated as weight in kilograms divided by height in meters squared.

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BP control. This is possible through focused strategies and changes in health care delivery.^19,22,28

Misdiagnosing of subjects with WCH can result in pre- scription of unnecessary lifelong treatment.²⁹ Patients diagnosed as having MH carry a risk comparable to that of persistent hypertension.³⁰ HBP alone is as reliable as combined clinic and ambulatory BP monitoring measurements in the monitoring of hypertension.³¹ Recent studies show that HBP tends to be superior to 24-hour ambulatory BP monitoring when discriminating individuals with increased cardiovascular risk.^32,33 If only those with elevated OBP had been invited to use HBP, we would have overlooked 240 persons (8%) who appeared to have MH. By contrast, in treated patients with normal OBP we found that 27% had elevated HBP (masked uncontrolled hypertension) which is similar to others’ findings.³⁴ We were not able to establish a certain

phenotypic person with MH or WCH. A recent study found the best OBP cutoff for diagnosing MH was 120/82 mm Hg.³⁵ By a cutoff OBP < 125/75, only 0.7% had MH in our study.

Likewise, by a cutoff OBP ≥165/115, only 0.7% had WCH.

Thus, using these limits in clinical practice MH and WCH can almost be ruled out and thereby optimizing the use of HBPM. Compared to prior studies we found a higher prevalence of WCH 18% vs. 13% (range 9–16%), but lower prevalence of MH 8% vs. 13% (range 10–17%).¹¹ This emphasizes the relevance of more widespread use of out of OBP measurements in the diagnosis and treatment of hypertension in Denmark.

By means of the questionnaire we only found 5% having diabetes. We found that 58% reach the HBP goals. This is far better than in previous Danish studies.¹⁷

Reduction of BP is closely related to reduction in cardiovascular morbidity and mortality.^2,36,37 A recent meta-analysis favors BP-lowering of 10/5 mm Hg by treatment even in grade 1 hypertension (140–159/90–99 mm Hg) in patients at low-to-moderate risk and not previously treated.³⁷ The meta-analysis showed a low numbers needed to treat (=29) for 5 years to prevent 1 major cardiovascular event.³⁷ In our study we found that a large number of participants had a slightly elevated BP, meaning that the prevalence of persistent hypertension fell from 27%(n = 838) to 8%(n = 244) by increasing the threshold of normotension by 10 mm Hg to OBP < 150/100 and HBP < 145/95. This finding shows that many of the participants had only slightly elevated BP.

Our study has several strengths. First, it is one of the larg- est prevalence studies using telemedical HBP measurements.

It illustrates clearly to what extent BP is controlled and how many undiagnosed hypertensive persons that may be found by HBP measurements. Second, most participants fulfilled the required schedule for the HBP measurements, namely

≥12 measurements on days 2 and 3 (3,102 of 3,159). The telemedical equipment was easy to use and had a high data security. If the monitor was not connected to the hub or cell phone coverage was lacking the equipment kept the measurements in its memory until connection was established.

Third, all attendees were asked to do HBP measurements not only those with a high OBP. Appropriate cuff sizes were used.³⁸ This makes it probably the most precise estimate of the prevalence of WCH and MH. Fourth, the possible difference between different monitors was largely eliminated by using the same BP monitor for the patient’s OBP and HBP.

Finally, patient reporting bias was eliminated by transmit- ting all the BP measurements telemedically. A study showed a precision of reporting HBP measurements of 76% (range 0–100%) and significantly more underreporting of the BP level than overreporting.³⁹

Our results may be influenced by a number of factors.

First, we only succeeded to include half of the possible population in the study. Second, in the municipality of Holstebro there have been prior telemedical HBP studies, which may have influenced the GP’s attention toward their patient’s BP.

Third, because of a planned integration to the electronic health records, we changed telemedical equipment halfway through the study by substituting the BP monitors A&D 767PlusBT¹³ with Omron 705IT. Both devices have been clinically validated according to the guidelines.^13,14 These

Table 3. Prevalence of masked and WCH according to different office blood pressure cutoff values with constant home blood pressure values (<135/85)

Office blood pressure

Prevalence MH

Prevalence WCH OBP < 120/70 0.3% (n = 8)

OBP < 125/75 0.7% (n = 22) OBP < 130/80 1.6% (n = 49) OBP < 135/85 3.9% (n = 122) OBP < 140/90 7.7% (n = 240)

OBP ≥ 140/90 18.1% (n = 560)

OBP ≥ 145/95 10.8% (n = 335)

OBP ≥ 150/100 5.6% (n = 174)

OBP ≥ 155/105 3.0% (n = 92)

OBP ≥ 160/110 1.7% (n = 52)

OBP ≥ 165/115 0.7% (n = 23)

OBP ≥ 170/120 0.3% (n = 10)

Systolic OBP < 120 1.5% (n = 46) Systolic OBP < 125 2.7% (n = 84) Systolic OBP < 130 5.1% (n = 158) Systolic OBP < 135 8.1% (n = 250) Systolic OBP < 140 11.4% (n = 355)

Systolic OBP ≥ 140 15.2% (n = 470)

Systolic OBP ≥145 9.7% (n = 301)

Systolic OBP ≥ 150 5.3% (n = 165)

Systolic OBP ≥ 155 2.8% (n = 88)

Systolic OBP ≥ 160 1.7% (n = 52)

Systolic OBP ≥ 165 0.7% (n = 23)

Systolic OBP ≥ 170 0.3% (n = 10)

Data are reported as percentage (number) of study participants.

In the upper part limits depending on systolic and/or diastolic blood pressure. In the lower part limits depending on systolic blood pressure.

Abbreviations: OBP, office blood pressure; WCH, white coat hypertension.

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devices have never been tested in direct comparison in a clinical setting, so minor differences due to different algo- rithms cannot be completely ruled out. However, by both

devices we found similar prevalences of normotension, WCH, MH, and persistent hypertension. Fourth, OBP was measured at a single visit, which may have influenced the

Table 4. Antihypertensive treatment, comorbidity, and risk factors in patients known with hypertension

Antihypertensive treatment

Controlled hypertension (n = 467)

Uncontrolled hypertension

(n = 483) P-value

No treatment^a 4% (n = 17) 11% (n = 52) <0.001

Mean number of antihypertensive drugs^a 2.0 ± 1.0 1.6 ± 1.0 <0.001

Angiotensin converting enzyme inhibitor^a 42% (n = 198) 38% (n = 184) NS

Angiotensin receptor antagonist^a 28% (n = 130) 23% (n = 111) NS

Calcium channel blocker^a 36% (n = 166) 34% (n = 162) NS

Thiazid^a 52% (n = 242) 42% (n = 205) <0.01

Furosemide^a 6% (n = 28) 4% (n = 19) NS

Spironolactone^a 3% (n = 14) 1% (n = 5) <0.05

Amiloride^a 1% (n = 5) 1% (n = 3) NS

Alpha-blocker^a 1% (n = 5) 1% (n = 7) NS

Beta-blocker^a 26% (n = 121) 19% (n = 93) <0.05

Minoxidil^a 0% (n = 0) 0% (n = 1) NS

Moxonidin^a 0% (n = 1) 0% (n = 1) NS

Male 46% (n = 215) 51% (n = 244) NS

Diabetes^a 14% (n = 66) 12% (n = 56) NS

Kidney disease^a 2% (n = 9) 2% (n = 7) NS

Prior ischemic heart disease^a 12% (n = 55) 7% (n = 33) <0.01

Prior stroke^a 6% (n = 28) 6% (n = 28) NS

Current smoker^a 15% (n = 69) 18% (n = 83) NS

Comparison of antihypertensive treatment in patients known with hypertension depending on whether the patient had controlled (HBP <

135/85) or uncontrolled hypertension (HBP ≥135/85). Data are reported as percentage (number) of study participants. Pearson’s chi-squared test used for comparisons of categorical variables. Student’s t-test used for comparison of unpaired continuous variables.

aSelf-reported data.

16%

30%

47%

62%

75%

11%

16%

18%

14%

9%

10%

8%

6%

3%

64%

44%

27%

14% 8%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

OBP<130/80

HBP<125/75 OBP<135/85

HBP<130/80 OBP<140/90

HBP<135/85 OBP<145/95

HBP<140/90 OBP<150/100 HBP<145/95 Normal OBP and normal HBP Elevated OBP and normal HBP

Normal OBP and elevated HBP Elevated OBP and HBP

Figure 2. Prevalence distribution of all study participants (n = 3,102) dependent on changing hypertension thresholds. Prevalence distribution according to normotension (normal OBP and normal HBP), WCH (elevated OBP and normal HBP), MH (normal OBP and elevated HBP), and persistent hypertension (elevated OBP and elevated HBP) dependent on changing hypertension thresholds. Abbreviations: OBP, office blood pressure; HBP, home blood pressure.

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accuracy of hypertension diagnosis in the office. Finally, for practical reasons we only used HBP measurements for 3 days in our study. However, adding more days does not change the conclusion regarding the HBP substantially.⁴⁰

In conclusion, one third of the age group 55–64 years had an abnormally high HBP, and one fourth had either WCH or MH. Our study is the first large-scale study to eliminate completely reporting bias by using telemedical transmission of BP data. Improvements in diagnosing and treating hypertension are necessary and telemedically transmitted HBP measurements may be an effective means to reach the goal.

ACKNOWLEDGMENTS

We thank participating citizens and the general practitioners Ulla & Jakob Hoffmann-Petersen; Helle Bondesen

& Jacob Houe; Marianne & Bent Conrad Pedersen; Susanne Schovsbo; Jørgen Buch, Dorte Navntoft & Ole Mecklenborg:

Mette Damgaard & Lotte Jakobsen; Poul Erik Hven; Kirstine Albrectsen, Karen Schou & Pernille Tørring; Michael Poulsen, Agathe Mierzwinska & Niels Christian Bentsen;

Annette Fleng & Jes Sørensen; Peder Kirkegaard; Anne Kristensen, Lene Kristensen, Tove Holm, Claus Larsen &

Kurt Ebbensgaard; Tina Høst & Finn Olsen; Trine Overgaard

& Anders Nissen; Ken Hermansen; Christian Thomsen;

Laila Andersen, Poul Bøge, Rita Christiansen, Allan Raft, Audun Bosnes and Tina Lundorff.

We thank study nurses Karen Markussen, Inge Winther, and Mona Godtkjær and laboratory technicians Susan Milton Rasmussen, Lisbeth Mikkelsen, Anne Mette Ravn, Kirsten Nygaard, and Henriette Simonsen for skillful assistance. We thank M.D. Janni Maigaard Jensen for helpful assistance during the recruitment. We thank Ellen Greve and Jesper Ejstrup from the municipal preventive care center for enthusiastic support.

The study was funded by the Tryg Foundation, Municipality of Holstebro, Central Denmark Region, and Research Fund of Central Denmark Region.

DISCLOSURE

The authors declared no conflict of interest.

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