Measuring your blood pressure at home: how to get a number that means something

What the top and bottom numbers are

The top number (systolic) is the pressure in your arteries at the moment your heart contracts. The bottom number (diastolic) is the pressure while your heart relaxes between two beats. Your monitor shows them as two numbers in millimetres of mercury (mmHg), the top number first.

Both numbers count. In people over fifty, the top number says most about the risk of heart and vascular disease. In younger people, a high bottom number is more often the first sign.

Blood pressure is not a fixed trait like your height. It responds to exercise, stress, coffee, a full bladder, temperature, talking and even to the measurement itself. At your GP’s it often comes out higher than at home. This is called the white-coat effect.

Why a measuring week

A single reading is a snapshot. Only a series of readings under the same conditions shows where your blood pressure usually sits.

That is why home measuring follows a fixed schedule. Ideally, measure seven days in a row. Measure every morning and every evening. Take two readings each time, one minute apart.

The readings from the first day do not count. They are often higher, because measuring is still new and a little tense. You take the average of the remaining readings. For that you need at least three days of readings after the first day.

In the morning, measure within an hour of getting up, after going to the toilet and before breakfast, coffee and any medication. In the evening, measure just before going to bed. Keep to roughly the same times every day.

How to measure reliably

Use a validated monitor with a cuff around your upper arm. A wrist monitor is more sensitive to posture. The cuff has to fit: a cuff that is too small gives a reading that is too high.

For half an hour beforehand, have no coffee, caffeinated drinks or nicotine, and do not exercise. Go to the toilet first.

Sit on a chair with a backrest. Put your feet flat on the floor and do not cross your legs. Sit still for five minutes, without your phone and without talking.

Rest your arm on a table so the cuff is at heart level. Put the cuff on your bare upper arm, about two fingers above your elbow.

Do not talk or move during the reading. After the first reading, wait a minute and measure again. Write down both values.

Always measure on the same arm. Choose the arm that gave the higher reading at your GP’s. If you do not know, use the arm you use least.

What the numbers mean

Trimetra follows the European guideline (ESC). It sorts the average of your home readings into three groups.

If your top number is below 120 and your bottom number below 70, your blood pressure is not elevated. From 120 to 134 on top, or from 70 to 84 at the bottom, it is elevated. From 135 on top or 85 at the bottom, it is high. Doctors call that hypertension.

The higher of the two numbers decides the group. An average of 128 over 86 is therefore high, even though the top number is not.

At home the limits are lower than in the consulting room. There, high starts at 140 over 90.

The group is not a diagnosis. Your GP also looks at your age, your other risk factors and sometimes a 24-hour measurement. If your average is elevated or high, discuss it with your GP. Bring your measuring week with you.

When not to wait

Is your top number 180 or higher, or your bottom number 110 or higher? Stay seated calmly and measure again after five minutes.

If the value stays that high, call your GP the same day. If the practice is closed, call the out-of-hours GP service. In Belgium, that is the GP on-call service on 1733.

Do you also have chest pain, shortness of breath, a severe headache, confusion, or trouble seeing, speaking or moving? Then call 112, or your local emergency number.

What Trimetra does with this

Enter a blood pressure reading under Log › Body values, or connect your monitor. Your blood pressure then appears on Overview. Tap it to start a seven-day measuring week. If you want to see what a change does, such as new medication or more exercise, you follow your blood pressure for four weeks.

You choose a morning and an evening time. If you have not measured that moment yet, you get a reminder around that time. Each time you enter two readings, or they come in from Apple Health, Health Connect or Withings. For morning and evening you see which days you have measured, and your average so far. Day 1 does not count.

After the last day you see your own average, top and bottom, and the group it falls into: not elevated, elevated or high. If it is elevated or high, it says to discuss the measuring week with your GP. If you measured on too few days, you see how many are needed.

Do you share a monitor with someone at home? If a reading from a connected app does not look like your own readings, or is very high, Trimetra asks whether it is yours. Until you answer, it does not count. If you choose no, you will not see it anywhere in Trimetra.

If a reading is very high, you see straight away that you should measure again after five minutes. If two readings are very high, you see that you should call your GP today, with a button to make the call. If such a reading comes in from a connected app, you get a notification.

Your blood pressure does not change your training plan. Trimetra gives no medical judgement. It lines up your readings so you can discuss them with your GP.

Frequently asked questions

One number says little, while measuring the same way for seven days says a lot. Trimetra lines up your measuring week, so you go to your GP with your own average.