Home blood pressure monitoring: how to measure, log and share your readings

Why measure blood pressure at home

Blood pressure changes through the day and with stress, activity, pain and even the experience of being in a clinic. Some people have higher readings at the doctor’s office than at home, sometimes called white-coat effect. Others look fine in clinic but have high readings at home, which is called masked hypertension. A set of readings taken calmly at home, in your usual routine, gives your doctor a fuller picture.

Home monitoring is commonly used to help diagnose high blood pressure, to check whether treatment is working, and to spot patterns such as a morning rise. It does not replace clinic visits. And it carries one rule above all: never change your medicines on your own because of a home reading. Share the readings with your doctor and let them decide.

Choosing a monitor and cuff

• Pick an automatic upper-arm monitor. Wrist and finger devices are generally less reliable, as they are sensitive to the position of the arm and hand.
• Choose a device that has been clinically validated for accuracy. Ask your doctor or pharmacist, or look for validation information from the manufacturer or an independent validation list.
• Get the right cuff size. A cuff that is too small gives falsely high readings, and one that is too large can give readings that are too low. Many monitors come with a medium cuff and offer larger ones, so measure your upper arm and compare it with the size range printed on the cuff.
• Check the device against the clinic. Take it to your next appointment and measure with the nurse’s equipment a few minutes apart to see whether the numbers agree.
• Replace worn cuffs and tubing, and follow the manufacturer’s battery and care instructions.

How to measure correctly

Small mistakes in technique can change a reading by 10 points or more. The following routine is based on guidance from bodies such as the NHS and the American Heart Association.

Before measuring:

• Avoid caffeine, smoking and exercise for at least 30 minutes beforehand, and empty your bladder.
• Sit quietly for five minutes with no phone, television or conversation.

During measurement:

• Sit upright on a chair with your back supported, feet flat on the floor and legs uncrossed.
• Rest your bare upper arm on a table so that the cuff is at the level of your heart. Do not measure over clothing, and make sure sleeves are not rolled so tightly they act as a tourniquet.
• Place the cuff according to the instructions, usually with its lower edge about 2 centimetres above the elbow crease.
• Stay still and do not talk while the cuff inflates and the reading is taken.
• Take two readings one minute apart and write down both.

Use the same arm each time unless your doctor has told you otherwise. If the readings differ markedly between arms at first, tell your doctor, and use the arm with the higher reading afterwards if advised.

When and how often

A common pattern for the days before a clinic review, in line with international guidance, is:

• Measure every morning (before taking medicines and before breakfast) and every evening (before dinner or medicines), taking two readings each time.
• Continue for seven days, or at least three, before the appointment.
• Your doctor will often discard the first day and average the rest.

Outside these periods, do not check constantly. Repeatedly measuring when you are worried can raise your blood pressure and your anxiety, and does not give useful information. Ask your doctor how often to continue after the initial period.

A log template

Keep a simple paper or phone note with these columns. Photographs of the monitor’s screen are also useful when you are not sure of your handwriting.

These two rows are example values only, to show the format. In the Notes column, write anything that could explain an unusual reading: a poor night’s sleep, pain, a cold, a new medicine, a salty meal or an argument. Note which medicines you took and when, since this helps your doctor interpret the pattern.

What the numbers mean

Readings are written as two numbers: systolic pressure (the higher number, when the heart beats) over diastolic pressure (the lower number, between beats), in millimetres of mercury (mmHg).

Different guidelines use slightly different thresholds. The NHS describes high blood pressure as 140/90 mmHg or higher in a clinic, and 135/85 mmHg or higher when measured at home. The World Health Organization defines hypertension in adults as 140/90 mmHg or above on repeated measurements. The American Heart Association and American College of Cardiology use a lower figure of 130/80 mmHg for stage 1 hypertension. Targets for people already treated vary with age, diabetes, kidney disease and other factors.

Home readings are usually a little lower than clinic readings, which is why the home threshold is lower. Rather than judging single readings against a table, your doctor looks at the average of the whole set and its relationship to your target.

When to seek urgent help

Do not wait for a routine appointment if a very high reading, such as 180/120 mmHg or above, comes with symptoms like chest pain, shortness of breath, severe headache, confusion, weakness or numbness on one side, difficulty speaking, a change in vision or severe back pain. Seek emergency care straight away; in India, call 112 or your local ambulance number.

If a very high reading appears without any symptoms, rest for five minutes and re-measure; if it remains high, contact your doctor the same day for advice. Very low readings with dizziness, fainting or weakness also deserve prompt medical advice, especially if you take blood pressure medicines.

Common mistakes to avoid

• Measuring straight after rushing, climbing stairs or being upset.
• Talking, scrolling on a phone or crossing the legs during the reading.
• Resting the arm below heart level, which gives falsely high readings.
• Taking only one reading and treating it as the truth.
• Choosing the “good” reading to write down. Record everything, as your doctor needs the honest pattern.
• Changing tablets, skipping doses or adding supplements because of the numbers.

What to bring to the doctor

Bring your log for the previous one to two weeks (or the monitor itself, if the readings are stored in it), a list of all your medicines with doses and times, and notes on symptoms such as dizziness, headaches, swelling or palpitations. If you take a salt-substitute product, herbal remedy or pain-killers regularly, mention it. Bring the cuff too if you would like your device checked against the clinic’s.

A short summary at the top of the page helps: “Average this week about 134/84; highest 148/92 on Tuesday after a poor night’s sleep; no dizziness.” You can use this approach for other measurements too, such as blood glucose, and our guide on preparing for a follow-up visit shows how to organise what you bring.

Special situations

• Pregnancy: blood pressure is checked at every antenatal visit, and home monitoring in pregnancy should only be done as advised by the obstetrician, who will tell you which readings need a call.
• Older adults and people who faint: your doctor may ask for a lying and then standing reading, because blood pressure can drop on standing. Do this only if advised, and have someone nearby in case you feel dizzy.
• Irregular heartbeat: some monitors give unreliable readings when the heartbeat is irregular. Mention it to your doctor and check whether the device you own flags an irregular rhythm.
• Children: they need a correctly sized cuff and a clinician’s guidance on what is normal for their age.

Questions worth asking your doctor

• What target should my home readings be under?
• For how many days, and at what times, should I measure before each review?
• Are my readings consistent with my clinic readings?
• Which readings should make me call you, and which mean I should go to an emergency department?
• Do I need any other checks, such as kidney tests or a lipid profile?

Sources

• World Health Organization: Hypertension fact sheet — definition, risks and global overview
• NHS: Blood pressure test — what the test is and checking at home
• NHS: High blood pressure (hypertension) — clinic and home thresholds
• American Heart Association: Home blood pressure monitoring — technique and schedule
• MedlinePlus: High Blood Pressure — NIH overview with links to related topics

A note on this guide

This guide is general information about measuring blood pressure. It is not medical advice, and it does not tell you what your target should be. Never change a medicine because of a home reading: discuss your readings with your doctor.