CLINICAL REVIEW For the full versions of these articles see bmj.com
Blood pressure self monitoring:
questions and answers from a
national conference
Richard J McManus,1 Paul Glasziou,2 Andrew Hayen,3 Jonathan Mant,4 Paul Padfield,5 John Potter,6
Emma P Bray,1 David Mant2
1
Primary Care Clinical Sciences, Self measurement of blood pressure was introduced in reduced earlier rather than later.5 6 The British Hyper-
University of Birmingham, the 1930s and is now practised by almost 10% of the tension Society recommends that hypertension is
Edgbaston Birmingham B15 2TT general population of the United Kingdom.1 2 Because
2
diagnosed by using a series of office blood pressure
Department of Primary Health blood pressure monitors are now readily available and
Care, University of Oxford,
readings taken over one to 12 weeks, depending on the
Headington, Oxford OX3 7LF cheap (as little as £10; €11.8; $15), self monitoring is blood pressure level.7 Self monitoring can provide more
3
Screening and Test Evaluation likely to increase—in the United States and Europe up to precise data in a much shorter time.
Program, School of Public Health, two thirds of people with hypertension self monitor.3 At
University of Sydney, NSW 2006
Australia
present we have insufficient evidence to make use of Improved accuracy
4
General Practice and Primary
multiple blood pressure readings generated from home Self monitoring can improve diagnostic and predictive
Care Research Unit, Institute of monitoring in clinical care. This review—which is based accuracy. A large cohort study in Japan showed that self
Public Health, University of on available evidence from randomised trials, systematic monitoring predicted the risk of stroke better than office
Cambridge, Cambridge CB2 0SR
5
reviews, and expert consensus—discusses the clinical readings. In this study, risk of stroke increased 29% (95%
Department of Medical Sciences,
University of Edinburgh,
importance of self measurement of blood pressure in confidence interval 16% to 44%) for each 10 mm Hg
Edinburgh EH4 2XU establishing the diagnosis of hypertension, in subsequent
increase in home systolic readings versus 9% (0% to 18%)
6
Faculty of Health, University of titration of drugs, and in longer term monitoring.
East Anglia, Norwich NR4 7TJ
for office readings.8 The predictive value of home
Correspondence to: R J McManus measurement improved with the number of measure-
What is self monitoring of blood pressure?
r.j.mcmanus@bham.ac.uk ments, with the best predictive value being seen with 25
Self monitoring of blood pressure is when a person (or
measurements.9 Another large cohort study used an
Cite this as: BMJ 2008;337:a2732 carer) measures their own blood pressure outside the
doi:10.1136/bmj.a2732 upper limit for normality of 135/85 mm Hg for self
clinic—at home, in the workplace, or elsewhere.4 Self
monitoring and found that each 10 mm Hg increase
monitoring allows multiple measurements and therefore
above this was associated with a 17% increase in risk of
provides a more precise measure of “true” blood pressure
and information about variability in blood pressure. cardiovascular disease, even when office blood pressure
was normal.10
What are the advantages and disadvantages?
Box 1 gives details of the potential advantages and Reduced risk
disadvantages of self monitoring. Self monitoring avoids two situations where office
readings can mislead—white coat hypertension, where
What is the value of self monitoring in diagnosis and out of home readings are normal but office readings are
prognosis?
Blood pressure can vary widely (fig 1). The main value of
self monitoring is that it can provide more precise Sources and selection criteria
estimates of the true underlying mean blood pressure We extracted key studies from a Medline search for
than traditional clinic measurements. The table shows the randomised controlled trials and systematic reviews to the
increased precision in mean systolic blood pressure end of 2007. These were supplemented by data from the
gained from additional measurements for up to two weeks. personal references of study group members. After an
open conference in early July 2008, at which the main data
Faster diagnosis from the literature were presented, the group held a
writing day to distil what was known and unknown for a
Trials have shown that morbidity and mortality are
series of questions for self monitoring of hypertension.
significantly lower in people whose blood pressure is
38 BMJ | 3 JANUARY 2009 | VOLUME 338
, CLINICAL REVIEW
raised, and masked hypertension, where the opposite is Date Time Systolic Diastolic Heart rate
Tips for non-specialists the case. Risk of death from cardiovascular disease pressure pressure (beats/min)
(mm Hg) (mm Hg)
Self monitored blood increases progressively from normal readings at home
pressure is lower than Day 1 8.31 135 72 56
and in the office, to white coat hypertension, then
office measured blood 8.25 144 76 58
masked hypertension, and finally increased readings at
pressure by about Day 2 8.14 133 73 57
home and in the office.11 Furthermore, one large cohort
10/5 mm Hg 8.08 162 69 59
study found that the prognosis for masked hyperten-
International guidelines sion was similar to that for uncontrolled office Day 3 8.27 155 78 51
suggest a threshold of hypertension.10 People with masked hypertension are 8.21 165 74 54
>135/85 mm Hg for
rarely identified, and self monitoring may be particu- Day 4 8.15 144 73 55
diagnosis of
larly helpful for this group, especially if it is used as a 8.09 156 78 58
uncomplicated
hypertension from self
screening tool for people with high-normal office Day 5 8.19 134 79 59
monitored blood readings.3 8.13 157 92 57
pressure and target for Day 6 8.25 163 78 57
treatment of Does self monitoring improve long term control? 8.19 167 75 57
≤135/85 mm Hg Several randomised trials have examined the effects of Day 7 8.20 128 69 59
European and US self monitoring on blood pressure but not clinical 8.14 151 72 60
guidelines recommend outcomes.12 A meta-analysis in 2004 reviewed 18
using the mean of two randomised controlled trials including 1359 people Fig 1 | Variation in one person’s blood pressure during one
home measurements with essential hypertension allocated to home blood week (two readings each day)
taken morning and pressure monitoring and 1355 allocated to the “con-
evening for a week after trol” group. Follow-up was between two and How does self monitoring reduce blood pressure?
discarding those 36 months.12 The meta-analysis showed small reduc- Better adjustment of antihypertensive drugs
readings from the first tions of blood pressure in the self monitoring group Doctors do not always treat patients with documented
day (4.3/2.4 mm Hg), but the true effect may be smaller as a raised blood pressure even though antihypertensives
result of publication bias. Self monitoring did not affect are known to reduce blood pressure and the risk of
the chances of achieving target blood pressure. cardiac disease.14-16 Self monitoring of blood pressure
Home monitoring alone seems to have only a may lead patients to discuss their blood pressure with
modest effect, and many studies of self monitoring their doctor and this may encourage appropriate
have included important cointerventions. These prescription of antihypertensives.
include patient education by lay people, nurses, or
pharmacists; telemonitoring or internet communica- Improved compliance with scheduled treatment
tion systems, with or without prompts; intensive nurse
Self monitoring makes patients more aware of their
led follow-up; and patient led titration of drugs.12 13
blood pressure level; this might increase their illness
Studies with additional cointerventions show a greater
perceptions and subsequent health behaviours and
effect size in the intervention arm.
therefore improve adherence to drugs. Of 11 rando-
mised controlled trials of self monitoring that reported
measures of treatment adherence, six showed a
statistically significant improvement in adherence,
but in five of these six trials self monitoring was part
Box 1 Advantages and disadvantages of self monitoring of blood pressure of a complex intervention.17 These trials must be
Potential advantages treated cautiously because pill counting was often used
The ability to take multiple measurements results in better estimation of “true” mean blood to measure compliance as opposed to more reliable
pressure for diagnosis and monitoring (reduces effect of inherent variability) methods.18
Better classification of blood pressure status—it removes the problems of white coat
hypertension and masked hypertension Improved non-pharmacological interventions
It empowers patients Self monitoring may lead to improvements in health
behaviours, such as diet and exercise, that help reduce
It is convenient for patients
blood pressure.15 A randomised controlled trial found
It may lead to better blood pressure control significant changes in body mass index at six and
Potential disadvantages
Measurements are hard to interpret because current evidence on risk of morbidity and
Effect of additional monitoring days on standard error of
mortality is based on office measurements
mean systolic blood pressure
Current treatment recommendations are based on office measurement
No of days Standard error of mean systolic blood pressure
It risks overmedicalising the population
monitored 2 readings/day 2 readings twice daily
Measurements may be inaccurate (poor technique, or poorly calibrated or validated
1 9.0 7.6
equipment)
3 6.6 6.0
Normal variation in blood pressure may cause anxiety in the patient 7 5.1 4.8
Requires motivation by patients and professionals 14 3.8 3.6
BMJ | 3 JANUARY 2009 | VOLUME 338 39
