Blood pressure target range: why the time within it counts

If you measure regularly, you end up with one number: the average. It goes into your blood pressure record, it is read out at the doctor's surgery, and it often decides the next step.

The average, however, has a property you cannot see at first glance. It is blind to the course over time. Two people with an identical average can have had completely different 24 hours. A large analysis from a Spanish registry of ambulatory measurements examined whether this difference has measurable consequences – the German Hypertension League (Deutsche Hochdruckliga) picked it up at the end of August.

What “target range” means here – and what it does not

First, a distinction, because two kinds of numbers are easily confused here.

Diagnostic thresholds answer the question of whether high blood pressure is present. They have not changed. The study's target corridor is something else: an analysis parameter the researchers used to calculate how much time a person spends within a defined window.

Number	Value	What it is meant for
Surgery measurement, threshold for hypertension	from 140/90 mmHg	Diagnosis
Home measurement, threshold for hypertension	from 135/85 mmHg	Diagnosis
Study target corridor, daytime	120–134 mmHg systolic	Analysis
Study target corridor, night-time	110–119 mmHg systolic	Analysis

You can find the full classification of thresholds in the blood pressure values table. The only important thing is: no personal treatment target can be derived from this study corridor. Which target value applies to you depends on age, other conditions and tolerability, and is set by your doctor.

Why the same average can hide two different courses

The idea behind it can be shown with a schematic example. Two people, both with a systolic 24-hour average of 128 mmHg:

	Person A	Person B
Systolic average	128 mmHg	128 mmHg
Course over 24 hours	stays almost continuously between 120 and 134 mmHg	swings between 105 and 155 mmHg
Time in corridor	high	low

Both bring the same number to their appointment. But Person B's circulation was outside the window for long stretches of the day – sometimes below, sometimes well above. The average erases exactly this information.

That a single reading says little is already well known; the reasons are explained in Why your blood pressure is different every time you measure. What is new is the question of whether even the average of many measurements still misses something essential.

What the analysis measured

The basis is a Spanish registry of 24-hour blood pressure measurements. It analysed 48,687 people (46 per cent women) who were either receiving blood-pressure-lowering treatment or had untreated high blood pressure.

• Follow-up: median 9.7 years
• During this period: 6,502 deaths, of which 2,185 were cardiovascular
• The researchers calculated the proportion of time systolic blood pressure spent within the corridor – 120 to 134 mmHg during the day, 110 to 119 mmHg at night

The result: the greater this proportion of time, the lower the mortality. Per increase of one standard deviation, all-cause mortality had a hazard ratio of 0.83 (95 per cent confidence interval 0.80 to 0.85), and cardiovascular mortality 0.80 (0.76 to 0.84).

A standard deviation is a statistical measure, not a percentage you could apply to your own log. The direction is nevertheless clear, and it is consistent across both endpoints.

The crucial point: it is not simply about fluctuations

This is the real core of the finding. One might object: anyone who spends a lot of time outside the corridor either has a higher average pressure or greater fluctuations – both have long been known to be unfavourable.

This is exactly what the researchers adjusted for. The associations remained even after adjusting for mean systolic blood pressure and for blood pressure variability. Time in target range therefore carries independent information – information contained neither in the average nor in the measure of variability.

That is why this analysis goes beyond yet another confirmation of what is already known.

Day and night have different corridors

It is striking that the study uses two different windows: 120 to 134 mmHg systolic during the day, 110 to 119 mmHg at night. This follows physiology. Blood pressure should fall during sleep, usually by 10 to 20 per cent compared with the daytime average.

If this dip does not occur, it is an independent risk factor – regardless of what the daytime values look like. This is covered in detail in Why your blood pressure at night matters more than during the day. For time in target range this means: a night-time profile that does not dip costs time share in a window that is narrower anyway.

What this means for your measurements at home

First, an honest limitation: home measurement cannot calculate this proportion of time. That requires continuous readings over 24 hours, i.e. ambulatory monitoring. Two readings a day do not make a course.

The perspective is still transferable. If you keep a measurement log over seven days – as described in When should you measure blood pressure? – do not just look at the average at the end:

• Count how many of your individual readings were within the target range, not just where the average ends up.
• Note outliers together with the situation instead of deleting them. A single high reading after an argument is different from a high reading at rest.
• Look for patterns over the day – regularly high morning values with good evening values are a clue worth following up.

A conspicuous log is a good reason to ask your doctor about 24-hour monitoring. No more – but no less either. The gap between the upper and lower value is also worth a look; what it tells you is explained in Pulse pressure: what the gap between your blood pressure values reveals.

What the finding does not show

This is an observational study based on a registry. It shows an association, not a cause-and-effect relationship. It does not follow that deliberately increasing time in target range lowers mortality – that would require intervention studies that actively use this proportion of time as a treatment target.

Nor does it imply any change to diagnosis or treatment. The thresholds remain as they are. And very explicitly: do not change any medication or the time you take it on this basis. The value of this analysis lies in how you read a measurement result – not in what you do as a consequence.

When you should seek medical advice

• If your average value is unremarkable but individual readings are regularly far above or below it
• If your morning values are repeatedly clearly above your evening values
• If your blood pressure does not reach the agreed target range despite treatment
• If you suspect your values do not fall at night – for example with loud snoring and observed pauses in breathing
• If you have known kidney disease or diabetes: here 24-hour monitoring is particularly informative

In case of sudden severe headache, chest pain, speech or vision problems or one-sided paralysis: call the emergency services on 112 immediately (the European emergency number).