Measuring & Tracking

24-Hour Blood Pressure Monitor on the NHS: What Happens, and What to Do With the Result

A cuff that inflates twice an hour while you are awake, and keeps going while you sleep, is nobody’s idea of a good time. It is also the most accurate blood pressure test the NHS has. Here is what the day involves, how the report is read, and what the numbers actually decide.

NK Medically reviewed by Dr Nouman Kazmi, MBBS, FCPS · 11 min read

2/hr

Readings taken while you’re awake

Minimum readings NICE averages

135/85

Daytime average that confirms a diagnosis

20/10

Gap that defines a white-coat effect

Key takeaways

Your GP ordered the monitor because NICE guideline NG136 asks them to. A clinic reading between 140/90 and 180/120 mmHg is a reason to investigate, not a diagnosis on its own.
The cuff takes at least two readings an hour while you are awake, and the diagnosis is built from the average of at least 14 of them.
Your 24-hour numbers will come back lower than the clinic ones. That is expected. The threshold that confirms hypertension on a daytime average is 135/85 mmHg, not 140/90 mmHg.
A gap of more than 20/10 mmHg between the clinic reading and the monitor average has a name: the white-coat effect. It is common, and it is the main reason this test exists.
One day is a snapshot. Whatever the report says, the useful measurement is what your readings do over the following weeks and months.

In this article

Why your GP ordered it
What the 24 hours are actually like
How the report is read
What “borderline” means
What happens after the result
The other 364 days
Where Daily Beets fits
Frequently asked questions
The bottom line

Why your GP ordered it

Nobody gets sent home with an ambulatory blood pressure monitor because their reading was fine. But it is worth being clear about what the referral means, because a lot of people read it as bad news when it is closer to the opposite.

NICE guideline NG136 tells GPs that if a clinic blood pressure sits between 140/90 mmHg and 180/120 mmHg, they should offer ambulatory blood pressure monitoring (ABPM) to confirm the diagnosis. The guideline is direct about why: ABPM is the most accurate method of confirming hypertension, and using it should reduce unnecessary treatment in adults who do not actually have it.

That last clause is the bit that matters. The monitor exists partly to stop people being put on medication they do not need. A single reading in a consulting room, taken by a stranger, with your sleeve rolled up and your morning behind you, is a genuinely poor way to characterise a system that changes minute to minute.

Worth knowing

Alongside the monitor, NG136 asks your GP to arrange checks for target organ damage and a formal cardiovascular risk assessment using QRISK. That usually means bloods, a urine test, an ECG and a look at the back of your eyes. If those get booked at the same time, it is the guideline being followed, not a sign that anyone is worried.

What the 24 hours are actually like

The NHS description is short: you go to a GP surgery, health centre or hospital to have the monitor fitted, and you bring it back the next day. It should not affect your daily activities. That is accurate, and it is about as much as fits on the page. Here is the longer version.

The fitting

A cuff goes on your upper arm, usually the non-dominant one, with a tube running to a small recorder that clips to your belt or sits in a pouch. It takes a few minutes. You will be shown how to keep the tube clear of your clothes and what to do if the cuff slips.

During the day

The cuff inflates and takes a reading at least twice an hour while you are awake, typically between about 8am and 10pm. When it starts, stop what you are doing, let your arm hang loose and stay still until it deflates. If you tense up or keep walking, the machine usually rejects the reading and tries again a minute later, so a fidget costs you two inflations instead of one.

Overnight

It keeps going, less often. Most people sleep through some inflations and wake for others. Poor sleep on monitor night is so common that it is worth mentioning at your follow-up rather than assuming it invalidates the whole test.

The practical bits worth knowing before the day starts

No shower or bath while it is on. The recorder is not waterproof.
Wear a loose top with sleeves you can get over the cuff.
Live a normal day. Go to work, do the shopping, walk the dog. A monitor worn during an artificially calm day measures an artificially calm day.
Keep the diary if you are given one. Noting a stressful meeting or a bad night gives whoever reads the report something to interpret the spikes against.

When not to wait: The monitor is a diagnostic test, not an emergency service. If you develop severe headache, chest pain, breathlessness, weakness or sudden visual changes while wearing it, contact NHS 111 or 999 as you normally would. NG136 asks for same-day specialist assessment where a clinic reading of 180/120 mmHg or higher comes with retinal haemorrhage, papilloedema or life-threatening symptoms.

The minimum number of waking readings NICE requires before an average can be used to confirm a diagnosis. What comes back is a whole day of readings with an average underneath, not one number. The average is what gets acted on.

How the report is read

You will probably see a graph with a scatter of dots, a day average, a night average and a 24-hour average. Almost everyone looks at the highest dot first. Almost nobody should.

The number that decides anything is the daytime average, and it is compared against a lower threshold than a clinic reading would be. NHS guidance puts it plainly: high blood pressure is 140/90 mmHg or higher when measured by a professional, and 135/85 mmHg or higher when measured at home. The monitor is measuring you in your normal life, so it is judged on the home-style threshold.

How NICE NG136 stages blood pressure using clinic and ABPM readings
Stage	Clinic reading	ABPM daytime average (or home average)
Stage 1	140/90 to 159/99 mmHg	135/85 to 149/94 mmHg
Stage 2	160/100 mmHg or higher, below 180/120	150/95 mmHg or higher
Severe	180 mmHg systolic or higher, or 120 mmHg diastolic or higher	Clinic reading alone; managed differently

If your daytime average comes back below 135/85 mmHg, the guideline does not confirm hypertension. That is not a clerical error and it does not mean the clinic reading was wrong. It means the clinic reading was one reading.

The white-coat effect, defined properly

NG136 gives it a number: a discrepancy of more than 20/10 mmHg between the clinic reading and the average daytime ABPM or home average, at the time of diagnosis. So a 158/96 in the surgery against a 134/84 daytime average is not a personality flaw or a wasted appointment. It is a recognised, named finding, and identifying it is one of the things the test is for.

What “borderline” means

“Borderline” is not a NICE category. It is what people say when a daytime average lands close to 135/85 mmHg, or in the lower half of stage 1, and the follow-up conversation ends with something like “we’ll keep an eye on it”.

That is a reasonable clinical position and a deeply unsatisfying one to be given, because it hands you a result without handing you an action. What it usually means in practice is this:

The average is genuinely near the line

Stage 1 on ABPM starts at 135/85 mmHg. A 137/86 and a 148/93 are both stage 1, and they are not the same situation. Ask which end of the band you are at.

Treatment depends on more than the number

For stage 1, the decision to offer medication takes account of your age, your QRISK cardiovascular risk estimate and whether there is evidence of target organ damage. Two people with identical averages can reasonably be given different advice.

“Keep an eye on it” means somebody has to keep the eye

In most practices that job quietly becomes yours between appointments. Which is fine, once you know that is the arrangement.

Three questions worth asking at the follow-up, written down before you go in: what was my daytime average, what did my QRISK score come out at, and what number would change your advice? A named threshold turns a vague review into something you can actually work towards.

What happens after the result

Broadly, three paths.

Hypertension confirmed. You will have a conversation about treatment, which may include medication depending on your stage, age and cardiovascular risk. Lifestyle advice comes alongside it, not instead of it. NG136 devotes a whole section to diet, exercise, alcohol, sodium and smoking, and none of it is optional filler.

Not confirmed, white-coat effect identified. No diagnosis today, and usually a recommendation to recheck within a defined period. Worth pinning down when, because this is the group most likely to fall out of the system entirely and turn up five years later with a higher number and no record of the intervening period.

Inconclusive or too few readings. If the monitor failed on too many attempts, or came off, you may be offered home blood pressure monitoring instead. NICE sets out that protocol clearly: two consecutive measurements at least a minute apart, seated, twice a day, morning and evening, for at least four days and ideally seven. The first day is discarded and the rest are averaged.

That home protocol is worth knowing regardless of which path you are on, because it is the same method you would use to build your own record afterwards.

The other 364 days

The monitor makes a point it never says out loud. The NHS did not put a cuff on your arm for a day because one reading is meaningful. It did it because one reading is not, and the only fix is more readings across ordinary life.

That argument does not stop being true when you hand the machine back.

A 24-hour test is a very good snapshot of one Tuesday. What it cannot show is the direction of travel: whether your average in November is higher than your average in June, whether the fortnight you cut back on ready meals moved anything, whether the number creeps every winter. Those questions need a record, and a record only exists if somebody keeps one.

The monitor makes the case for trends. It just does not stay on your arm long enough to show you one.

Using the same NICE home protocol, morning and evening, a couple of days a week, gets you there. Paper works. A spreadsheet works. So does the BP Tracker, which is free to use, keeps the readings in one place and leads on a rolling 7-day and 28-day average rather than the last number, which is the one thing a paper notebook is genuinely bad at. It will also produce a printable report you can hand to your GP.

Free to use · Sign in to start logging

Keep the trend, not just the readings

The BP Tracker logs morning and evening readings and leads on your rolling 7-day and 28-day averages rather than the number from this morning. It exports a printable report for your GP. Built by Matter, free to use, and yours.

Open the BP Tracker → Free to use · Printable GP report

Whatever you use, bring it to the follow-up. A printed fortnight of paired morning and evening readings gives whoever is making the decision far more to work with than a memory of what the machine said in the summer.

Where Daily Beets fits

Somewhere below the monitor, the medication conversation and the food shop. Which is the honest place for it.

Daily Beets is a food supplement, not a treatment, and nothing in it is a substitute for anything your GP recommends. It is a UK-formulated capsule. The biggest thing in it is hibiscus extract at 700mg a serving, then grape seed at 200mg, then concentrated beetroot extract and a four-vitamin B complex. Thiamine contributes to the normal function of the heart. Folate, vitamin B6 and B12 contribute to normal homocysteine metabolism. Those are authorised claims, which is a polite way of saying they are the ones we are allowed to make and can stand behind.

It is for people already doing the measurable things and wanting something steady to take alongside them. Two capsules a day, and enough weeks for a trend to mean something.

Daily Beets by Matter

The daily bit, for the other 364 days

Concentrated beetroot, hibiscus and grape seed extract with a four-vitamin B complex, designed to support normal cardiovascular function as part of a varied diet. Two capsules a day. 90-day guarantee.

Try the 90-Day Protocol → 12 ingredients · Cardiologist-reviewed

Frequently asked questions

What is a 24-hour blood pressure monitor on the NHS?

It is ambulatory blood pressure monitoring, or ABPM. A cuff on your upper arm is connected to a small recorder you wear for a day, and it takes readings automatically while you go about normal life. The NHS fits it at a GP surgery, health centre or hospital and you return it the next day. NICE guideline NG136 recommends it when a clinic reading falls between 140/90 mmHg and 180/120 mmHg, because it is the most accurate way to confirm whether someone actually has hypertension.

How many readings does a 24-hour blood pressure monitor take?

NICE asks for at least two measurements an hour during your usual waking hours, for example between 8am and 10pm, and the diagnosis is made from the average of at least 14 of those waking readings. Most monitors continue overnight at a lower frequency. If too many individual readings fail, the average may not be usable and you may be offered home monitoring instead.

What is a normal result from a 24-hour blood pressure monitor?

The number that matters is the daytime average, and it is judged against a lower threshold than a clinic reading. NHS guidance describes high blood pressure as 140/90 mmHg or higher when measured by a professional and 135/85 mmHg or higher when measured at home. A daytime average below 135/85 mmHg does not confirm hypertension under NG136. Averages of 135/85 to 149/94 mmHg fall into stage 1, and 150/95 mmHg or higher into stage 2.

Can I shower or sleep with a 24-hour blood pressure monitor on?

You sleep with it on, and the monitor keeps recording overnight at a lower frequency. You cannot shower or bathe with it, because the recorder is not waterproof. Wear a loose-sleeved top, keep the tube clear of your clothing, and when the cuff starts to inflate let your arm hang still until it deflates. Broken sleep on monitor night is common and worth mentioning at your follow-up.

Why is my 24-hour average lower than the reading at the surgery?

Usually the white-coat effect, and NICE defines it precisely as a discrepancy of more than 20/10 mmHg between the clinic reading and the average daytime ABPM or home average at the time of diagnosis. It is common, it is recognised, and identifying it is one of the reasons the test is offered. It does not mean the clinic reading was taken badly, and it does not mean you can stop paying attention. It means the single reading was not representative.

What should I do while I wait for my 24-hour monitor results?

Start your own record using the NICE home protocol: two consecutive readings at least a minute apart, seated, twice a day, morning and evening, for at least four days and ideally seven, discarding the first day and averaging the rest. Keep doing the lifestyle basics NG136 sets out around diet, sodium, activity, alcohol and smoking. Do not change or stop any prescribed medication while you wait, and contact NHS 111 or 999 if you develop severe headache, chest pain, breathlessness or sudden visual changes.

The bottom line

A 24-hour monitor is an uncomfortable day that buys you a much better answer than the one you had. The average is the result, not the highest dot. The threshold is 135/85 mmHg, not 140/90 mmHg. And a gap between the surgery and the report has a name and a number attached to it.

Whatever it comes back as, the argument the test is built on still holds the day after you hand it back. One reading is a moment. A trend is information. The NHS just proved that to you with a piece of equipment, which is a better argument than anything we could write.

Continue learning

References

National Institute for Health and Care Excellence. Hypertension in adults: diagnosis and management (NG136), recommendations 1.2.5, 1.2.6, 1.3.3, 1.5.2 and section 1.4. Available at: nice.org.uk/guidance/ng136
National Institute for Health and Care Excellence. Hypertension in adults: diagnosis and management. Full guideline, NCBI Bookshelf NBK547161 (definitions of stage 1, stage 2 and severe hypertension; white-coat effect). Available at: ncbi.nlm.nih.gov/books/NBK547161
NHS. Blood pressure test. Available at: nhs.uk/tests-and-treatments/blood-pressure-test
NHS. High blood pressure (hypertension). Available at: nhs.uk/conditions/high-blood-pressure-hypertension

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