A blood pressure reading has two numbers. The top (systolic) number is the pressure when your heart pumps. The bottom (diastolic) number is the pressure when your heart relaxes between beats. A healthy reading is usually between 90/60mmHg and 120/80mmHg, and the NHS considers 140/90mmHg or higher (135/85mmHg or higher at home) to be high.
What do the two blood pressure numbers mean?
Blood pressure is measured in millimetres of mercury (mmHg) and written as one number over another, for example 128/82.
- Systolic (top number): the highest pressure in your arteries, when your heart squeezes and pushes blood around your body.
- Diastolic (bottom number): the lowest pressure in your arteries, between heartbeats, when your heart is resting and refilling.
Both numbers matter. Your clinician will look at both, and a raised reading in either one can be important.
What are the UK blood pressure ranges?
The table below uses NHS and British Heart Foundation ranges for most adults under 80. Home readings tend to be a little lower, so they have a lower threshold.
| Category | Reading | What it usually means |
|---|---|---|
| Low | Below 90/60mmHg | Often harmless, but may cause dizziness or fainting in some people |
| Normal | 90/60mmHg to 120/80mmHg | The healthy range for most adults |
| Slightly raised | Above 120/80mmHg but below 140/90mmHg | Not high blood pressure, but may mean you are at risk of developing it, so worth keeping an eye on |
| High (clinic, GP or pharmacy) | 140/90mmHg or higher | Possible high blood pressure (hypertension) that needs confirming |
| High (home reading) | 135/85mmHg or higher | Possible high blood pressure that needs confirming |
These ranges are a general guide. Thresholds are different for people aged 80 and over, where the target is usually below 150/90mmHg in a clinic or below 145/85mmHg at home. Targets can also differ for for people with conditions such as diabetes or kidney disease, so your clinician will advise on what is right for you. You can read more on the NHS high blood pressure page.
Why does high blood pressure matter?
High blood pressure rarely causes symptoms, which is why many people do not know they have it. Over time, it puts extra strain on your heart, blood vessels, kidneys and eyes. Left untreated, it raises the risk of heart attack, stroke and heart failure.
It is easy to measure and can often be managed with lifestyle changes, medicine or both.
What is white-coat hypertension?
White-coat hypertension is when your blood pressure is higher in a clinic than it is in everyday life. It happens because being with a doctor or nurse can make you feel anxious, even if you do not notice it.
It matters because:
- A single high clinic reading may lead to a diagnosis of high blood pressure that is not accurate.
- You might be offered medicine you do not need.
- Your clinician still needs to know about it, as some people with white-coat hypertension go on to develop raised blood pressure later.
The opposite can also happen. Some people have normal readings in the clinic but higher blood pressure at home or at work. This is called masked hypertension, and it can be missed without readings outside the clinic.
Why is 24-hour ambulatory monitoring (ABPM) used to confirm a diagnosis?
If a clinic reading is 140/90mmHg or higher, NHS guidance is to confirm it with readings taken outside the clinic before diagnosing high blood pressure. The two usual ways are home monitoring and 24-hour ambulatory blood pressure monitoring (ABPM).
ABPM is often seen as the most reliable way to confirm the diagnosis because:
- It takes many readings: the monitor checks your blood pressure automatically, at least twice an hour during your usual waking hours and less often at night. NICE guidance uses the average of at least 14 daytime readings, and with a clinic reading of 140/90mmHg or higher, a daytime average of 135/85mmHg or higher confirms high blood pressure.
- It reflects your normal life: readings are taken while you work, travel, relax and sleep, rather than in one stressful moment.
- It shows your night-time pattern: blood pressure normally dips while you sleep. ABPM shows whether this happens, which a clinic or home reading cannot.
- It helps spot white-coat and masked hypertension: comparing your daytime average with clinic readings can show whether nerves are affecting your results.
ABPM can also be useful if you already take blood pressure medicine and your clinician wants to see how well it is working across the whole day.
What happens during a 24-hour blood pressure test?
Here is what to expect:
- A cuff is fitted to your upper arm and connected to a small monitor that you wear on a belt or strap.
- You go about your normal day. The cuff tightens every so often to take a reading, then loosens again.
- When the cuff inflates, try to keep your arm still and relaxed by your side.
- You may be asked to note down activities, symptoms and when you went to bed and woke up.
- After 24 hours, the monitor is removed and the readings are analysed.
You usually cannot shower or bathe while wearing the monitor, so it helps to wash beforehand. Wear a loose top with roomy sleeves. You can read more in our guide to 24-hour ambulatory blood pressure monitoring.
Tips for getting an accurate reading at home
These steps help you get reliable home readings:
- Use a validated, upper-arm monitor with the right cuff size.
- Sit quietly for five minutes first, with your back supported and feet flat on the floor.
- Rest your arm on a table at about heart level.
- Avoid eating, caffeine, smoking and exercise for about 30 minutes before, as they can raise your reading for a short time.
- Take two readings a minute apart, morning and evening, for as many days as your doctor or nurse advises, and write them all down.
When should you seek urgent help?
Call 999 straight away if you have chest pain, collapse, severe breathlessness, or signs of a stroke such as face drooping, arm weakness or slurred speech. If you have a very high reading with symptoms such as a severe headache, blurred vision or confusion, get urgent medical help. For other worries, speak to your GP or call NHS 111.
Frequently asked questions
What is a normal blood pressure for an adult?
A healthy blood pressure is usually between 90/60mmHg and 120/80mmHg for most adults. Your clinician may set a different target depending on your age and health.
Is 140/90 high blood pressure?
A clinic reading of 140/90mmHg or higher suggests possible high blood pressure. It is usually confirmed with home readings or 24-hour ambulatory monitoring before a diagnosis is made.
Can anxiety raise my blood pressure reading?
Yes. Feeling nervous in a clinic can raise your reading for a short time. This is known as white-coat hypertension, and ABPM can help show whether it is affecting your results.
Does a 24-hour blood pressure monitor hurt?
No. The cuff squeezes firmly for a few seconds during each reading, which can feel a little uncomfortable.
Can I sleep with an ABPM monitor on?
Yes, and you should. Night-time readings are an important part of the test, as they show whether your blood pressure dips normally while you sleep.
Do I need a GP referral for a 24-hour blood pressure test?
Not at The Heart Clinic. You can book yourself in directly, and GP or specialist referrals are also welcome.
Booking a blood pressure test with The Heart Clinic
The Heart Clinic offers 24-hour ambulatory blood pressure monitoring for £175, including the test, clinical review and a written report, usually within 24 working hours, with Consultant Cardiologist oversight. You can visit our Luton clinic or book a home visit across London, Hertfordshire and Buckinghamshire. See our prices or contact us to book.