How to track your blood pressure properly at home

A single reading tells you almost nothing. A week of readings taken the same way tells you a great deal. Blood pressure moves constantly — with posture, caffeine, conversation, a full bladder, the time of day — so the technique matters as much as the monitor.

Before you measure

• Sit quietly for five minutes first. Not thirty seconds. Five.
• Empty your bladder. A full bladder raises readings measurably.
• No caffeine, exercise or smoking for 30 minutes beforehand.
• Sit with your back supported and both feet flat. Legs uncrossed.
• Rest your arm on a table at roughly heart height. An unsupported arm reads high.
• Do not talk during the measurement. Talking raises readings.

Cuff size and placement

A cuff that is too small reads high, sometimes substantially. Check the sizing guide that came with your monitor against your upper arm circumference. Place the cuff on bare skin, not over a sleeve, with the lower edge about two centimetres above the elbow crease.

How many readings, and when

Take two readings a minute apart and record both, or use the average if your monitor offers one. Do this at the same two times each day — morning before medication and food, and evening — because readings follow a daily rhythm and comparing a morning number to an evening one tells you nothing.

Average the week, not the day

This is the part people skip, and it is the part that matters. Any single reading can be unusually high or low for reasons that have nothing to do with anything you are testing. Record everything, then compare weekly averages.

A low reading on a Tuesday is noise. A lower weekly average across three consecutive weeks is a signal worth paying attention to.

Change one thing at a time

If you start a supplement, cut your salt, begin walking and improve your sleep in the same fortnight, you will have learned something good about your health and nothing at all about the supplement. Hold everything else steady while you test one variable.

What to do with the numbers

Take them to your doctor. A log of home readings is genuinely useful clinical information — far more useful than a single measurement taken in a clinic, where readings often run high for reasons of nerves alone. MedlinePlus explains what the numbers mean.

When to stop logging and call someone

If you record a very high reading, or if you have symptoms such as chest pain, severe headache, vision changes or shortness of breath, this stops being a tracking exercise. Contact a medical professional. A log is for trends, not for emergencies.