Blood pressure measurement
Also known as: blood pressure test, blood pressure check, ambulatory blood pressure monitoring, home blood pressure monitoring
The pressure of blood against the artery walls, recorded as two numbers: the systolic pressure when the heart contracts and the diastolic pressure between beats. Measured with a cuff on the upper arm, it is the most frequently taken measurement in medicine because raised blood pressure usually causes no symptoms yet drives heart attacks, strokes and kidney disease.
- Abbreviations
- BP
- Kind
- Physiological measurement
- Categories
- Vital signs & physiological measurements, Cardiovascular, Point-of-care & home testing
- Specimen
- No specimen
- Method
- Physical measurement
- Terminology
- LOINC 85354-9, 8480-6, 8462-4
- Type
- Physiological measurement
- Sample
- None: a cuff on the upper arm
- Used for
- Screening for and diagnosing hypertension, monitoring treatment, assessing dizziness on standing
- Measures
- Systolic and diastolic arterial pressure in mmHg
- Result
- Two numbers in mmHg, read against guideline thresholds; averaged home or ambulatory readings for diagnosis
Why is it used?
- Routine health checks and screening for hypertension
- Confirming a raised clinic reading with ambulatory or home monitoring
- Monitoring blood-pressure treatment
- Dizziness on standing, when lying and standing readings are compared
- In pregnancy, kidney disease, diabetes and after a stroke or heart attack
What does it measure?
| Measure | What it tells you |
|---|---|
| Systolic pressure | The peak pressure as the left ventricle ejects blood, in mmHg. |
| Diastolic pressure | The lowest pressure, while the heart refills, in mmHg. |
| Ambulatory monitoring (ABPM) | Readings taken automatically over 24 hours by a worn cuff; the daytime average is the reference measurement for diagnosing hypertension. |
| Home monitoring (HBPM) | Twice-daily readings taken by the person over several days with a validated arm cuff, averaged. |
A high or low value can be associated with several different situations; the result is interpreted with other results, symptoms, history and clinical findings.
How is it performed?
Seated and rested for a few minutes, arm supported at heart level, a correctly sized cuff on the upper arm; readings are repeated and the average used. Ambulatory monitoring uses an automatic cuff worn for 24 hours; home monitoring uses a validated upper-arm device morning and evening for several days.
Specimen. None
Do I need to prepare?
Avoid caffeine, smoking and exercise for 30 minutes before; empty the bladder; sit quietly with the back supported and legs uncrossed; do not talk during the reading.
What do the results generally mean?
| Finding | What it may indicate |
|---|---|
| Clinic reading raised | Hypertension is suspected but not diagnosed: ambulatory or home monitoring confirms it, because clinic readings are often higher than usual (white-coat effect) |
| Ambulatory or home average above the diagnostic threshold | Hypertension; the stage, cardiovascular risk and any organ damage guide lifestyle advice and treatment |
| Very high reading with symptoms | Severe hypertension or an emergency; assessed the same day |
| A fall on standing | Postural (orthostatic) hypotension, a common cause of dizziness and falls, often from medicines or dehydration |
Guideline thresholds
| Threshold | Value | Unit | Applies to | Country · source |
|---|---|---|---|---|
| Clinic blood pressure suggesting hypertension | 140/90 or higher | mmHg | A clinic reading at or above this prompts ambulatory (or home) monitoring to confirm the diagnosis | UK UK |
| Ambulatory or home average confirming stage 1 hypertension | 135/85 or higher | mmHg (daytime average) | Diagnosis of stage 1 hypertension when the clinic reading is 140/90 or higher | UK UK |
| Stage 2 hypertension | 160/100 or higher (clinic), 150/95 or higher (ABPM/HBPM average) | mmHg | Treatment is offered to adults of any age with stage 2 hypertension | UK UK |
Clinical decision thresholds come from the named guideline and country; they are not laboratory reference intervals, and they change when guidance changes.
What can affect the result?
- Cuff size, arm position, talking, a full bladder and recent caffeine, smoking or exercise
- The clinic setting itself (white-coat effect) and, conversely, masked hypertension that is normal in clinic but raised at home
- Pain, anxiety, cold and the time of day
- Medicines: decongestants, NSAIDs, steroids, oral contraceptives and stimulants raise it; antihypertensives, some antidepressants and alcohol change it
Medicines. Antihypertensive medicines are what the measurement monitors; NSAIDs, decongestants, corticosteroids and some antidepressants can raise it.
What can the test not tell you?
- Whether arteries or organs have been damaged, which needs blood tests, urine tests, an ECG and sometimes imaging
- The cause of high blood pressure, which is usually not identifiable and occasionally due to kidney, adrenal or other disease
- Blood pressure inside the heart or lungs, which needs catheter studies
A single reading is a poor guide: blood pressure varies minute to minute, and diagnosis rests on averaged out-of-clinic readings. Wrist and finger devices are less reliable than validated upper-arm cuffs, and irregular rhythms such as atrial fibrillation make automatic devices inaccurate.
Other tests commonly used with it
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.