Measuring blood pressure: right or left arm? The clear answer
Both arms the first time, then always the one with the higher readings. And the difference between arms is itself a finding that many people overlook.
The answer in three sentences: Measure on both arms the first time. After that, always stick with the arm that shows the higher readings. A persistent difference of more than 15 mmHg should be checked by a doctor.
That answers the question. What is more interesting is why this is the case – because the reasoning also explains why the wrong choice systematically misleads you.
Why the higher arm counts
Almost everyone has a small difference between their arms – a few mmHg is completely normal. It arises from differences in vascular anatomy: the artery to the right arm branches off the aorta differently from the one to the left.
What counts is the higher reading, because it comes closer to the actual pressure in the circulation. The lower arm underestimates it. So anyone who chooses the “more pleasant" arm will rate themselves too favourably for years – without noticing, because the readings look consistent.
In practice this means: you make this decision once. After that, always use the same arm, otherwise your readings are no longer comparable with each other.
The difference itself is information
This is where it gets medically interesting. A persistent difference between sides of more than 15 mmHg in the upper reading is not just a measuring curiosity, but can indicate a narrowing in one of the supplying arteries. In large analyses, such a difference is associated with increased cardiovascular risk.
This is a finding you only come across if you look for it specifically once. Anyone who only ever measures one arm from the start will never discover it.
Important: a single comparison is not enough. Measure both arms on three different days. The difference only counts if it is reproducible.
How to compare both sides correctly
- Sit quietly for five minutes, back supported, legs uncrossed.
- Measure on the first arm. Cuff at heart level, correct size.
- Wait one to two minutes, then measure on the second arm.
- Then measure on the first arm once more. The average of the two measurements on the first arm is fairer, because blood pressure usually falls slightly over the course of a session.
- Repeat on two more days.
Step 4 is almost always left out and is the most common reason for apparent differences between sides that are not real.
When you cannot freely choose the arm
In some situations a particular arm is avoided. These include a dialysis shunt, removal of lymph nodes on that side, a recent injury or an intravenous line. If one of these situations applies to you, follow your doctor's instructions – regardless of which arm shows the higher readings.
Where you measure matters more than which arm
Two common mix-ups that cause bigger errors than the choice of side:
Upper arm instead of wrist. Validated upper-arm monitors are recommended for self-measurement, because wrist monitors react much more sensitively to arm position. Details in Measuring blood pressure at the wrist.
Cuff at heart level. Ten centimetres below gives around 7.5 mmHg too much – more than most differences between sides. All seven common mistakes are listed in Measuring blood pressure correctly.
When you should seek medical advice
- If there is a reproducible difference between sides of more than 15 mmHg
- If one arm hurts or tires quickly during exertion
- If one arm feels cold, pale or numb
- If your weekly average on the relevant arm is at or above 135/85 mmHg
In case of sudden severe headache, chest pain, speech or visual disturbances or one-sided paralysis: call the emergency services on 112 immediately.
How to describe your symptoms so your doctor can actually work with them
Five steps for your next doctor’s appointment – plus a printable template for noting down your observations.
This is how it usually sounds
“I felt strange again last night. A kind of stumble, and it gave me a fright.”
“Let’s keep an eye on it.”
The guide shows you how to describe it instead and which questions to ask. What is usually missing are the numbers from exactly those two minutes – and those are what the BPER records, beat by beat.
Frequently asked questions
Which arm should I measure my blood pressure on?
On both the first time. After that, always on the arm that shows the higher readings. You make this decision once and then stick with it, so that your readings remain comparable.
Why does the higher reading count rather than the lower one?
Because it comes closer to the actual pressure in the circulation. Anyone who chooses the arm with the lower readings will permanently rate themselves too favourably without noticing.
At what difference between sides should I see a doctor?
From more than 15 mmHg in the upper reading, if the difference is reproducible on several days. It can indicate a narrowing in a supplying artery.
Why do I often measure lower on the second arm?
Because blood pressure usually falls slightly over the course of a measuring session. That is why you should measure twice on the first arm – before and after the second arm – and compare the average.
Are there situations in which an arm should not be used?
Yes, for example with a dialysis shunt, after removal of lymph nodes on that side, with recent injuries or an intravenous line in place. In that case, follow your doctor's instructions.
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This article is for general information only and does not replace a medical diagnosis or treatment. If you have symptoms or questions about your treatment, please consult your doctor.