Vital Signs

Blood Pressure

Also written as: BP

The force of blood against artery walls, recorded as a systolic and a diastolic pressure.

What it measures

Two pressures inside the arteries, written as one number over another. The systolic (top) number is the pressure while the heart contracts and pushes blood out. The diastolic (bottom) number is the pressure while the heart relaxes and refills between beats.

Why it is checked

Checked at nearly every medical visit because persistently raised pressure quietly strains the heart, blood vessels, kidneys, and brain over years, usually without symptoms. Repeated readings over time matter far more than any single measurement.

What is generally associated with a higher result

Broadly associated, when persistently elevated across many readings, with hypertension and with age-related stiffening of the arteries. Isolated high readings are extremely common and are broadly associated with stress, pain, caffeine, a full bladder, and the clinic environment itself.

What is generally associated with a lower result

Broadly associated with dehydration, blood loss, certain medications, and some hormonal conditions. Naturally low readings without any symptoms are common, particularly in younger and physically fit people, and are generally not pursued.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

• A cuff that is too small or too large for the arm, which skews the reading
• Caffeine, nicotine, or exercise shortly before the measurement
• Talking during the reading, or an arm that is unsupported or not at heart level
• The white-coat effect, meaning readings that run higher in medical settings than at home
• A full bladder, crossed legs, or skipping a few minutes of quiet rest beforehand

Questions to take to your appointment

• Was the cuff the right size for my arm?
• Would home readings or a monitor worn over a full day give a clearer picture than office readings?
• What is the correct way to position myself when measuring at home?
• How many readings, over how long, are needed before drawing any conclusion?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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