What is a 24-hour blood pressure monitor?
It’s a cuff you wear for a day. It checks your blood pressure by itself, about every half hour by day. But one number decides if your blood pressure is high.
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What is a 24-hour blood pressure monitor?
It’s a cuff on your upper arm, joined by a tube to a small box on a belt. You wear it home and take it back the next day.
Doctors call it ambulatory blood pressure monitoring, or ABPM. Ambulatory just means you’re up and about.
You’re usually offered one after a high reading at the surgery. NICE says to offer it if your clinic blood pressure is between 140/90 and 180/120, to confirm whether you have high blood pressure.
Your 24-hour test, step by step
- 1
Fitted
At a GP surgery, health centre or hospital.
- 2
By day
The cuff checks about every half hour.
- 3
By night
It checks about every hour while you sleep.
- 4
Back next day
Your readings go to the doctor who asked for the test.
Sources: NHS; North Bristol NHS Trust
The NHS says wearing it will not affect your daily activities. So live your normal day. That’s the day your doctor wants to see.
What is it like to wear an ambulatory blood pressure monitor?
You’ll feel the cuff squeeze. Some people get a tingle in the arm while the cuff fills. It goes when the cuff lets go.
How to get a good 24-hour reading
- Shower or bath before your appointment.
- Wear a top with wide or loose sleeves.
- When the cuff starts to fill, sit if you can, keep your arm still and stay quiet.
- Wear the monitor day and night for the whole time.
- Don’t bath, shower or swim while you wear it.
- Keep taking your medicines as normal, unless your doctor says otherwise.
Missed reading? The box tries again after about 5 minutes by itself. You can use your phone.
Need to drive? Clinics differ.
North Bristol advises driving only to and from the appointment. Royal Berkshire says drive as normal and don’t drop your arm. Ask your clinic which applies.
What does my ABPM result mean?
That one number is your daytime average. NICE uses the average of at least 14 readings taken while you’re awake. That’s why you may be asked when you get up and go to bed.
NICE confirms high blood pressure if your clinic reading was 140/90 or higher and your daytime average is 135/85 or higher.
- Below 135 mmHgBelow 135. Not confirmed if your bottom number is also below 85.
- 135 to just under 150 mmHgNICE stage 1, with a clinic reading of 140/90 to 159/99.
- 150 mmHg or aboveNICE stage 2, with a clinic reading of 160/100 to under 180/120.
Source: NICE NG136
| Result | Clinic reading | Daytime average |
|---|---|---|
| Not confirmed | 140/90 or higher | Below 135/85 |
| Stage 1 | 140/90 to 159/99 | 135/85 to 149/94 |
| Stage 2 | 160/100 to under 180/120 | 150/95 or higher |
Source: NICE NG136
The monitor records at night too. But NICE bases the diagnosis on the daytime average. Ask your doctor for your daytime average, both numbers.
More on the stages in stage 1 and stage 2 high blood pressure.
Why is the ABPM number lower than the clinic one?
NICE says the matching numbers for ABPM are 5 lower than for clinic readings. That’s why it’s 135/85, not 140/90. The NHS uses 135/85 for home checks as well.
A clinic reading is one photo. A 24-hour test is a film of your normal day. A tense minute in the surgery can spoil one photo, but it’s a few frames of a film.
So a high clinic reading and a daytime average below 135/85 means NICE does not confirm high blood pressure. If your clinic reading is more than 20/10 above your daytime average, NICE calls it a white-coat effect, if this shows when you’re first diagnosed. Read more in white coat hypertension.
Can’t wear the cuff overnight? NICE says to offer home checks instead if ABPM doesn’t suit you. Here’s how to take readings at home.
What happens after the 24-hour test?
Your readings go to the doctor who asked for the test. You’re usually told at your next appointment, or a letter goes to your GP.
Not confirmed? NICE says to check your clinic blood pressure at least every 5 years, and maybe more often if it’s under 140/90 but still raised.
Confirmed? Your GP will talk through what helps, and you may be offered more 24-hour or home checks if your clinic and daytime numbers don’t match.
If you’re being treated, NICE aims for a daytime average below 135/85 if you’re under 80, and below 145/85 if you’re 80 or over. Your GP may set a different aim if you’re frail or have several conditions.
Never stop or change a prescribed medicine without your prescriber.
Questions to ask when you get your results:
- What was my daytime average, both numbers?
- Was it 135/85 or higher?
- Did my clinic and daytime numbers differ by more than 20/10?
- When should my blood pressure be checked again?
To read each number on the report, see blood pressure readings explained.
When to speak to a GP
High blood pressure does not usually cause symptoms. The only way to know is to get it checked. Speak to your GP or the clinic if:
- You can’t wear the cuff for the full 24 hours. Ask about home checks instead.
- You haven’t heard about your results.
- You’re 40 or over and haven’t had your blood pressure checked for more than 5 years.
- You often have headaches or blurred vision, have chest pain that comes and goes, or have other symptoms you’re worried could be caused by high blood pressure. Get help from NHS 111.
Call 999 if you have sudden chest pain that does not go away. It can feel like squeezing, pressure, burning or indigestion.
Also call 999 if pain spreads to your arm, neck, jaw, stomach or back, or comes with feeling sweaty, sick, light-headed or short of breath. Don’t drive yourself to A&E.