High Blood Pressure (Hypertension) - Tests

How is blood pressure measured?

Blood pressure is measured in millimetres of mercury (mm Hg).

Clinic/GP surgery blood pressure readings: these are readings taken by a doctor or nurse in a clinic or GP surgery, using a standard blood pressure machine.

Home blood pressure readings: these are readings taken by a person whilst seated and at rest at home, using a standard blood pressure machine. You need to take readings twice a day for a week. This will give 14 top and 14 bottom readings. Add the top readings together and divide by 14. Then do the same for the bottom readings. This gives you an average reading. It's normal for your blood pressure to fluctuate, so a single raised reading isn't a cause for concern unless it's extremely high.

Ambulatory blood pressure readings: these are readings taken at regular intervals whilst you go about your normal activities. A small machine that is attached to your arm takes and records the readings, usually over a 24-hour period.

As a rule, an average of the ambulatory blood pressure readings gives the most true account of your usual blood pressure. Home blood pressure readings are a good substitute if an ambulatory machine is not available. Ambulatory and home readings are often a bit lower than clinic or GP surgery readings. Sometimes they are a lot lower. This is because people are often much more relaxed and less stressed at home than in a formal clinic or surgery situation.

What is high blood pressure?

High blood pressure (hypertension) is a blood pressure that is 140/90 mm Hg or above each time it is taken at the GP surgery (or home or ambulatory readings where the average is more than 135/85 mm Hg). That is, it is sustained at this level. High blood pressure can also be:

  • Just a high systolic pressure - for example, 170/70 mm Hg.
  • Just a high diastolic pressure - for example, 120/104 mm Hg.
  • Or both - for example, 170/110 mm Hg.

However, it is not quite as simple as this. Depending on various factors, the level at which blood pressure is considered high enough to be treated with medication can vary from person to person.

Blood pressure of 140/90 mm Hg or above (or average home/ambulatory readings 135/85 mm Hg or above)

If your blood pressure is always in this range you will normally be offered treatment to bring the pressure down, particularly if you have:

  • A high risk of developing cardiovascular diseases (see below); or
  • An existing cardiovascular disease (see below); or
  • Diabetes; or
  • Damage to the heart or kidney (end-organ damage) due to high blood pressure.

Blood pressure of 160/100 mm Hg or above (or home/ambulatory readings 150/95 mm Hg or above)

If your blood pressure is always in this range, you will almost certainly be advised to have treatment to bring it down.

Blood pressure between 130/80 mm Hg and 140/90 mm Hg

For most people this level is fine. However, current UK guidelines suggest that this level is too high for certain groups of people. Treatment to lower your blood pressure if it is 130/80 mm Hg or higher may be considered if you:

  • Have developed a complication of diabetes, especially kidney problems.
  • Have had a serious cardiovascular event such as a heart attack, transient ischaemic attack (TIA) or stroke.
  • Have certain ongoing (chronic) kidney diseases.
Next: Causes

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Author:
Dr Mary Harding
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
4271 (v45)
Last Checked:
19 December 2016
Next Review:
19 December 2019
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