Journal of Human Hypertension (1999) 13, 817–822
 1999 Stockton Press. All rights reserved 0950-9240/99 $15.00
http://www.stockton-press.co.uk/jhh
ORIGINAL ARTICLE
Clinical implications of white coat
hypertension: an ambulatory blood
pressure monitoring study
G Manning1, L Rushton2 and MW Millar-Craig1
1
Division of Vascular Medicine, Derbyshire Royal Infirmary, Derby, UK; 2Institute for Environment and
Health, Leicester University, Leicester, UK
Within routine clinical practice, white coat hypertension
(where blood pressure is persistently higher in the presence of the doctor or nurse but normal outside the medical setting) makes the diagnosis and management of
hypertension difficult. There are conflicting data regarding the prevalence and significance of white coat hypertension. This study has used ambulatory blood pressure
monitoring to detect the presence of white coat hypertension in 186 patients referred to an out-patient hypertension unit. The presence of white coat hypertension
was defined as an average office blood pressure
(measured on three occasions over a 2-month period)
of ⬎140/90 mm Hg and an ambulatory awake blood
pressure ⱕ136/86 mm Hg. The prevalence of white coat
hypertension in those patients with borderline hypertension (diastolic blood pressure 90–99 mm Hg) and those
with mild-to-moderate hypertension (diastolic blood
pressure ⱖ100 mm Hg) was determined. Echocardiography was used to assess left ventricular mass index in
patients with and without white coat hypertension. The
prevalence of white coat hypertension in the total group
was 23%. However, the prevalence was higher (33%) in
those patients with borderline hypertension compared
to 9% of those patients with mild-to-moderate hypertension. There was a statistically significant increase in left
ventricular mass index in patients with no evidence of
white coat hypertension (125 gm/m2) compared to those
with white coat hypertension (102 gm/m2). We conclude
that, if office blood pressure is used to identify patients
with hypertension who may require treatment, some
patients will be incorrectly diagnosed and may be
treated inappropriately. We recommend that ambulatory
blood pressure monitoring is used in the routine
assessment of all newly diagnosed hypertensive
patients. Furthermore, we recommend echocardiography in patients with borderline hypertension as some
will already have an increased left ventricular mass
index.
Keywords: white coat hypertension; borderline hypertension; left ventricular hypertrophy
Introduction
Hypertension is common in the general population
and, whilst standard blood pressure measurements
by cuff are of value in large populations, it is welldocumented that they might be unreliable in individuals.1 Blood pressure may vary between consecutive measurements over short periods or when measured at different times, often, but not always,
resulting in a fall in blood pressure over time.2 The
diagnosis of hypertension and the decision to
initiate antihypertensive medication is often difficult given this inherent variability of blood pressure.
Clinicians are often presented with patients who
initially have raised blood pressure that subsequently falls over a period of time or that varies
considerably between visits; patients with ‘labile’
blood pressure. The reduction in blood pressure
over time may be due to specific non-pharmacological measures initiated by the patient such as salt
Correspondence: Dr Gillian Manning, Division of Vascular Medicine, Derbyshire Royal Infirmary, London Road, Derby DE1
2QY, UK
Received 23 March 1999; revised and accepted 14 July 1999
restriction, weight reduction or an increase in physical activity.
The additional problem of white coat hypertension, where blood pressure is persistently higher in
the presence of the doctor or nurse but normal outside the medical setting, makes the diagnosis and
management of hypertension difficult.3 White coat
hypertension has an estimated prevalence ranging
from 12% to 53% dependent upon the population
studied and definition used.4,5 The definition of an
elevated office blood pressure is usually taken as
⭓140/90 mm Hg but the definition of a normal out
of hospital blood pressure varies. This variation can
produce marked differences in the prevalence and
significance of the condition.6
The causes and consequences of the white coat
effect have not yet been fully elucidated. Whilst it
has been reported that the magnitude of the effect is
greater in some patients in the presence of a physician as opposed to a nurse, other studies have
shown that nurse measured blood pressure is not a
reliable indicator.7 There are also conflicting data
regarding the relationship of the white coat effect to
gender and age.7 Several cross-sectional studies
have shown that patients with white coat hyperten-
White coat hypertension and left ventricular mass
G Manning et al
818
sion have a lower incidence of target organ damage
than those who show no white coat effect, but data
from other studies is at variance with these findings.8,9 There is evidence from a small number of
studies that patients with white coat hypertension
have a lower risk of cardiovascular events than those
without. However, there is also evidence to show
that some patients may be in a prehypertensive state
and a proportion of patients with white coat hypertension may develop hypertension requiring treatment.10,11
The overall aim of the present study was to evaluate the use of ambulatory blood pressure monitoring
in the assessment of white coat hypertension in routine clinical practice by: (i) determining the prevalence of white coat hypertension in patients with
suspected hypertension referred to an out-patient
hypertension clinic, (ii) comparing the prevalence of
white coat hypertension, in borderline and
mild/moderate hypertension, and (iii) measuring
left ventricular mass index in patients with and
without white coat hypertension.
Patients and methods
All patients, both male and female, referred to the
out-patient hypertension unit, during the period
April 1992 to September 1998 who were not currently receiving antihypertensive medication and
had not been on antihypertensive medication in the
previous year, were included.
Blood pressure was measured in the hypertension
unit using a calibrated mercury sphygmomanometer
according to British Hypertension Society guidelines on three occasions over a 2-month period.12
Three measurements of blood pressure were made
on each occasion, after 5 min rest, with the subject
sitting or lying. At least 1 min was allowed between
each measurement and the mean of three measurements was taken as the ‘office blood pressure’. The
mean blood pressure from the three visits was
defined as the average screening blood pressure.
Patients with an average blood pressure ⭓140/90
mm Hg underwent baseline investigations.
Baseline investigations
Lifestyle, including smoking, alcohol and exercise,
was documented using an investigator completed
questionnaire. A clinical history was taken for
cardiovascular disease including myocardial
infarction, angina, stroke, transient ischaemic
attacks, diabetes, peripheral vascular disease and
asthma. Drug history, current medication and family
history of cardiovascular disease were documented.
Demographic data included gender, age (years),
height (centimentres) and weight (kilograms).
Ambulatory blood pressure
Non-invasive ambulatory blood pressure was measured using the Medilog Ambulatory Blood Pressure
recorder (Medilog ABP) which has previously been
shown by the authors to meet the accuracy criteria
of the Association for the Advancement of Medical
Instrumentation.13 The Medilog ABP measures
blood pressure by the detection of Korotkoff sounds
via a transducer taped over the brachial artery.
Accuracy to ±6 mm Hg was determined prior to each
recording by simultaneous blood pressure measurement, lying down and standing.
The recorder was set to measure blood pressure
either at 30-min intervals for 24 h or 15-min intervals from 07.00–18.00 and 30-min intervals thereafter. Patients were instructed to make additional
blood pressure measurements using the manual
start/quit facility on the recorder if their arm was
moving during the measurement. Patients were
encouraged to return to their normal daily activities
for the duration of the recording. A diary card was
used to detail activities during the recording period,
in particular the awake and asleep time, and to provide information and advice on the procedure to
the subject.
The data from the recorder were transferred to a
computer for analysis. Data analysis was undertaken
using the commercial software supplied by the
manufacturers. Recordings in which 20% or more
of the measurements failed were rejected and those
patients were encouraged to return for a repeat recording. The mean awake and asleep blood pressures
were calculated based on diary times, which has
been shown to reflect more accurately patient awake
and asleep cycles.14 The presence of white coat
hypertension was defined as a raised office blood
pressure, taken as the average screening blood pressure ⭓140/90 mm Hg, and normal ambulatory awake
blood pressure ⭐136/86 mm Hg (2 standard deviation upper limit of normal from previously published normal data study).15
Echocardiography
Echocardiography was undertaken with the subject
carefully positioned in the partial (30– 45°) left lateral decubitus position with the transducer placed
in the third to fifth intercostal space. Left ventricular
dimensions were measured from the parasternal
short axis view just below the level of the mitral
valve. Left ventricular end-diastolic internal dimension, interventricular septal thickness and posterior
wall thickness in diastole were measured from three
cardiac cycles during quiet expiration according to
the Penn convention. The Penn convention enddiastolic measurements are taken at the peak of the
R wave and exclude the endocardial echoes from the
interventricular septal wall, posterior wall and
include them in the left ventricular dimension.16
Recordings were made at 50 mm/sec, with the
ECG positioned to allow accurate measurement at
the R wave peak. Recordings that were technically
difficult, with poor visualisation of the cardiac structures, were not included. Left ventricular mass
index was calculated according to method described
by Deveraux corrected for body surface area.16 Left
ventricular hypertrophy was defined as a left ventricular mass index ⬎110 gm/m2 in females and
⬎132 gm/m2 in males.16
On completion of the baseline investigations,
patients attended the out-patient clinic and
White coat hypertension and left ventricular mass
G Manning et al
underwent further investigation for secondary
hypertension as clinically indicated. Nonpharmacological advice was given, as required, with
regard to smoking, alcohol intake, weight, cholesterol, exercise and salt intake. Those requiring dietary advice were referred to the dietician.
Results
A total of 332 patients were referred during the
recruitment period, 103 patients currently being
treated for hypertension were excluded. A further
43 patients were excluded as not meeting the office
blood pressure criteria (36), failing to attend
appointments (5) or intolerance of the blood pressure recorder (2). The remaining 186 patients, 95
males and 91 females, comprised the study group.
The majority (93%) of patients had never received
antihypertensive medication and in the 7% who had
previously received therapy none had done so in the
previous 12 months. Three patients had a history of
cardiovascular disease (one myocardial infarction,
two transient ischaemia attacks). No patients had
any ECG evidence of atrial fibrillation. The mean age
of the group was 46 (range 18–71) years, height 1.7
(range 1.42–1.93) metres and weight 78 (45–152) kilograms.
The baseline mean screening blood pressure was
higher 161/101 mm Hg than the ambulatory awake
blood pressure 145/91 mm Hg of the group. These
data, together with the data for asleep and overall
ambulatory blood pressure, are shown in Table 1.
Average screening systolic blood pressure was
higher than ambulatory awake blood pressure in 164
(88%) and average screening diastolic blood pressure was higher in 169 patients (91%). Using the
definition described in the methods section 42
patients had white coat hypertension (prevalence
23%).
The patients were divided into two groups: borderline hypertension (defined as an average screening diastolic blood pressure 90–99 mm Hg) and
mild/moderate hypertension (⭓100 mm Hg). Ninetyeight (53%) of patients were classified as borderline
hypertensives and 88 (47%) patients as
mild/moderate hypertensives. Comparison of the
groups showed an increase in prevalence of white
coat hypertension in the borderline hypertensives
32 (33%) compared to 8 (9%) of the mild/
moderate hypertensives.
The total group was then divided into those with
white coat hypertension (n = 42) and those without
(n = 44) and the groups compared. The groups were
similar in age (45 vs 48 years, P = NS) but the white
coat hypertensive group had a higher proportion of
females (55% vs 47%, P = ⬍0.05) Both screening
and ambulatory blood pressures were significantly
lower in the group with white coat hypertension, as
shown in Figure 1.
Echocardiography was available in 168 patients
(in 18 (10%) patients technically acceptable recordings could not be obtained). Left ventricular
diastolic dimension was similar in both groups. The
group with white coat hypertension had a lower
interventricular septal thickness, posterior wall
thickness and left ventricular mass index than those
where white coat hypertension was absent and these
comparisons
reached
statistical
significance
(P ⬍ 0.05). These results are shown in Table 2.
Only eight patients with white coat hypertension
had an increase in interventricular septal thickness
⬎1.2 cm (18%) compared with 55 patients (38%) in
the group who showed no white coat effect. Left
ventricular mass index was increased (females ⬎110
and males ⬎132 gm/m2) in 9% of the white coat
group compared to 44% in the non-white coat
group.
Discussion
Within routine clinical practice it is important to
identify patients with a raised blood pressure in the
Table 1 Average screening and 24-h ambulatory blood pressure
in 186 patients with suspected hypertension
Systolic
Diastolic
(mm Hg)
(mm Hg)
Mean (s.d.) Mean (s.d.)
Screening blood pressure
Ambulatory awake blood pressure
Ambulatory asleep blood pressure
Ambulatory overall blood pressure
161
145
121
138
(19)
(16)
(19)
(16)
101
91
73
86
(8)
(10)
(12)
(10)
Figure 1 Average screening and 24-h ambulatory blood pressure
in patients in the absence (n = 144) 䊐 and presence (n = 42) 䊏 of
white coat hypertension. (Mean systolic and diastolic ±1 standard deviation).
819
White coat hypertension and left ventricular mass
G Manning et al
820
Table 2 Echocardiographic measurements from 186 patients with
suspected hypertension in the presence or absence of white
coat hypertension
White coat hypertension
Left ventricular diastolic
dimension
Interventricular septal
thickness
Posterior wall thickness
Left ventricular mass
index
P
Present
(n = 42)
Mean (s.d.)
Absent
(n = 144)
Mean (s.d.)
4.9 (0.5)
5.0 (0.6)
1.05 (0.02)
1.21 (0.02) ⬍0.001
0.83 (0.02)
102 (23)
0.89 (0.02) =0.05
125 (33)
⬍0.001
NS
surgery and a normal blood pressure at other times
as these patients are likely to be managed differently
to those with sustained blood pressure elevation.
These patients essentially have office hypertension
and ambulatory normotension. The term ‘white coat
hypertension’ has traditionally been used to
describe this scenario where patients exhibit an
acute elevation of blood pressure that is induced by
the presence of a doctor and this term is still widely
used not only by hospital physicians and general
practitioners but also by patients themselves. However, more recently the terms ‘isolated clinic hypertension’ or ‘isolated office hypertension’ have been
used to describe these patients. This term takes
account of the fact that it is not exclusively the
white coat of the physician which causes the difference in office to daytime blood pressure but that
other factors including daytime activity are
involved.4,17,18 Ambulatory blood pressure monitoring is a reliable, non-invasive technique to measure
out-of-hospital blood pressure and many general
practices now undertake it within their own practice
or by referral to specialist centres.
White-coat hypertension is common with a prevalence of 23% in this group of patients, which is similar to that found in other studies in different populations, but it is important to recognise differences
between reported studies.4,5 These differences may
relate to variations in the populations studied or
may reflect the differing criteria used to define white
coat hypertension, including cuff-off points and
methods of calculation of both office and ambulatory blood pressure.6
The prevalence of white coat hypertension in
patients with borderline hypertension was, perhaps
not unsurprisingly, found to be higher (33%) than
in those with mild/moderate hypertension. Whilst
the prevalence of borderline hypertension varies
dependent upon the definition used (some studies
using blood pressure alone, others including evidence of target organ damage), there are convincing
data to show that the prevalence increases with age
and may be as high as 40% by the age of 60.19 There
is also evidence to suggest that the level of blood
pressure as a juvenile predicts future blood pressure.
Therefore, those starting with a blood pressure level
at the higher end of the normal range are more likely
to progress to borderline hypertension.20 Patients
with borderline hypertension will be common in
general practice and the use of 24-h blood pressure
monitoring to identify those subjects with a normal
out-of-hospital blood pressure who may not initially
require antihypertensive medication but will require
regular follow-up is important. It is recognised that
the definition of a ‘normal out-of-hospital blood
pressure’ is still subject to some debate as there are
no large-scale prospective epidemiological studies
available.
White coat hypertension has implications for the
management and treatment of patients with hypertension, and also cost implications, which need
further work. It is, however, likely that the measurement of out-of-hospital blood pressure using
ambulatory blood pressure monitoring will become
commonplace.21
Several cross-sectional studies have shown that
patients with white coat hypertension have a lower
incidence of target organ damage, as has been shown
in the present study, but there are other studies
which have refuted this.8,22 There are few long-term
studies of patients with white coat hypertension, but
the evidence from two studies suggests that patients
with a lower ambulatory blood pressure have a
lower risk of subsequent fatal or non-fatal cardiovascular events than those with more elevated
ambulatory blood pressure, and have a good prognosis similar to those with normotension.10,23
However, data from the Cornell study indicated
that white coat hypertension is associated with a
risk between that of normotension and hypertension, and a study by Alderman et al found that
hypertensive patients with a blood pressure higher
when taken by a doctor than a nurse had a higher
risk of myocardial infarction during a 14-year follow-up period.24,25 There is also evidence that treating patients with white coat hypertension, before
they have developed hypertension on ambulatory
recording, may not confer benefit but result in the
overtreatment of hypertension.26
Studies looking at the response of white coat
hypertensives to laboratory stresses have demonstrated that these patients do not score higher on
reactivity scales measuring anger or anxiety and it
has been suggested that the white coat response is a
learned condition response.27 Fear might originally
induce an increase in blood pressure and subsequently the awareness of hypertension determine
an increased sympathetic arousal at each visit, and
this response may be benign. In others, it may be
an alarm response and it may occur in response to
everyday stresses the patient encounters.28
This study has demonstrated that some patients
with only small elevations of blood pressure already
have evidence of left ventricular hypertrophy. Left
ventricular hypertrophy is an important independent risk factor for cardiovascular disease in
both normotensive and hypertensive populations
and risk increases progressively with the degree of
left ventricular hypertrophy.29 When detected by
echocardiography, left ventricular hypertrophy has
been shown to have a prevalence of 16% in males
and 21% in females, the prevalence increasing with
White coat hypertension and left ventricular mass
G Manning et al
age. Some studies have shown an independent
increase in left ventricular mass with age from 8%
in males under 30 years to 33% in those age 70 years
or more; similarly for females the increase is from
5% to 49%.30 However, it is recognised the lower
left ventricular mass index in those patients with
‘white coat hypertension’ may reflect differences in
blood pressure levels, rather than the white coat
effect per se.
Echocardiography is a technique that allows the
reliable, non-invasive estimation of left ventricular
mass. Previously, most physicians have relied on the
ECG to detect the presence of LVH. However, the
ECG has been found to be specific but insensitive in
the detection of LVH compared to echocardiography.31 The findings from this study show that a
small proportion of patients with white coat hypertension may have echocardiographic left ventricular
hypertrophy (9%). In view of the implications of the
presence of left ventricular hypertrophy,32 echocardiography should be considered in patients with
white coat hypertension to detect the presence or
absence of left ventricular hypertrophy and thus target treatment at patients with documented target
organ damage. It has been suggested that in these
circumstances a limited echocardiographic study
would be appropriate.33
Whether these patients with ‘white coat hypertension’ require treatment at diagnosis remains a clinical dilemma and there is continuing debate as to
whether it is an innocent phenomenon or whether
it carries an increased cardiovascular burden.34 We
would recommend that these patients have a full
assessment of cardiovascular risk and, in line with
current guidelines, those at high risk or with documented target organ damage should be considered
for treatment.35 Guidelines from New Zealand have
recommended treating those patients with uncomplicated mild hypertension and a cardiovascular
event risk of 2% per year (20% over 10 years).36
Those patients at low cardiovascular risk should
be followed up on a regular basis and at present we
would suggest that their blood pressure should be
measured at least every 6 months by the practice
nurse. There is insufficient evidence to support precise guidelines for the follow-up of these patients
but our current practice is to re-assess cardiovascular risk annually and consider a further 24-h blood
pressure recording in those patients whose office
blood pressure has risen.
Conclusion
If office blood pressure alone is used to identify
patients with hypertension it will result in some
patients being incorrectly diagnosed and treated
inappropriately. It is recommended that 24-h ambulatory blood pressure monitoring be used in the routine assessment of all newly diagnosed hypertensive
patients. Furthermore, limited echocardiography
should also be considered as some patients with
only borderline hypertension will already have an
increased left ventricular mass.
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