Blood pressure at home: what the second number means

Why two readings differ

Almost everyone reads higher the first time. The cuff is unfamiliar, you have just walked in from the car, and the act of being measured raises the number by five to ten points on its own. This is consistent enough that we build it into the process: three readings a minute apart, and the first is discarded before anything is written down.

At home the effect is smaller but it does not disappear. If you sit down, roll up a sleeve and take a reading straight away, you are measuring the arrival as much as the blood pressure. Five minutes of sitting still before the cuff goes on is the single change that makes a home log worth reading.

The other half of the gap is real variation. Blood pressure moves through the day — lowest in the small hours, highest mid-morning, up again after coffee, food, cold, a full bladder or a difficult phone call. One number is a snapshot of one moment. A week of them is a pattern, and the pattern is what gets treated.

A single reading is a snapshot. A week of them is a diagnosis.

What the second number actually is

The top number, systolic, is the pressure while the heart is pushing. The lower one, diastolic, is the pressure left in the arteries while the heart refills — the floor your circulation never drops below. It gets less attention than it deserves. In people under about fifty a raised diastolic is often the first thing to appear, sometimes years before the systolic moves at all.

What counts as raised depends on where it was measured. Home readings run lower than clinic readings, so the thresholds are lower too: 135/85 at home is roughly the same finding as 140/90 in the room. If you bring us a log, tell us which monitor and which arm, and we will read it against the right line.

Measuring properly at home

Sit for five minutes with your back supported and both feet on the floor. Rest the arm on a table so the cuff sits level with your heart. Do not talk. Take two readings a minute apart and write both down, morning and evening, for seven days — the first day is usually the worst and we ignore it.

Use an upper-arm monitor rather than a wrist one, and bring it in once so we can check it against ours. A monitor that is two years old and has never been compared to anything is a monitor that might be reading eight points off in either direction.

When to call us, and when not to

One high reading is not an emergency and is not worth a phone call. A week of readings averaging above 135/85 is worth an appointment, but a routine one.

What is worth calling about is a reading above 180/120 that stays there when you repeat it after five minutes of rest, or any reading at all that arrives with chest pain, sudden breathlessness, weakness on one side, difficulty speaking or a change in vision. Those are not blood pressure questions any more, and they belong with urgent care or an ambulance rather than with a log.

What we do with your log

We average it, discard the first day, and compare it against your last set. Most of what we are looking for is direction rather than a single value: whether a change six months ago did anything, whether the mornings are consistently worse than the evenings, whether a number that looked alarming in the room looks ordinary at home.

Bring the log to your appointment, on paper or in the portal. Two readings a day for seven days is plenty — morning before medication, evening before bed — and we would rather have seven honest days than a month of tidy ones.