Why Is Blood Pressure Different in Each Arm? UK Guide
Blood pressure can be different in your left and right arms. Small differences may occur because readings naturally vary and measurement technique is not always identical. However, a repeated difference matters. NICE recommends measuring blood pressure in both arms when considering a diagnosis of hypertension. If the difference is more than 15 mmHg, repeat the measurements. If it remains above 15 mmHg, use the arm with the higher reading for subsequent checks and discuss the finding with a healthcare professional.
Why can blood pressure differ between arms?
Blood pressure is not a fixed number. It changes from moment to moment with breathing, stress, activity and posture. Because home readings are normally taken one arm after the other rather than simultaneously, a change in your blood pressure between readings may look like a difference between arms.
Measurement differences can also arise when the cuff is positioned differently, one arm is unsupported, the cuff is the wrong size, or you move or talk during a reading. In some people, a consistent difference may reflect differences in blood flow through arteries. A home monitor cannot determine the cause.
What does NICE say about a difference between arms?
NICE guideline NG136 gives a clear approach for clinicians considering a diagnosis of high blood pressure:
- Measure blood pressure in both arms.
- If the difference between arms is more than 15 mmHg, repeat the measurements.
- If the difference remains more than 15 mmHg on the second measurement, use the arm with the higher reading for future measurements.
This recommendation relates to the difference in readings, particularly systolic blood pressure (the top number). It is not a way to diagnose a blocked artery at home. A persistent difference is a reason to tell your GP or practice nurse so they can consider it in the wider clinical picture.
How to check both arms at home
- Sit quietly for at least five minutes in a chair with your back supported and feet flat on the floor.
- Avoid talking during measurements. Rest the arm on a table with the cuff at heart level.
- Use a suitable upper-arm cuff on bare skin and follow the monitor's instructions.
- Measure one arm and record the result, including which arm you used.
- After a short rest, measure the other arm using the same posture and cuff positioning.
- If the results differ, repeat the comparison rather than drawing conclusions from a single pair of readings.
- Share a persistent difference with your GP or practice nurse, particularly if the higher reading is also raised.
Because sequential measurements can change with time, a clinician may repeat or assess them under more controlled conditions. Do not keep checking excessively if repeated readings are making you anxious.
Which arm should you use for future blood pressure readings?
If a repeated difference above 15 mmHg is confirmed, NICE advises using the arm with the higher reading for subsequent blood pressure measurements. Consistency is important when comparing readings over days and weeks. Record which arm you used so a clinician can interpret your home diary.
If you have already been told to use a particular arm because of surgery, a vascular access device or another medical reason, follow your clinical team's instructions rather than switching arms on your own.
What if one arm is 120 and the other is 140?
For example, if the systolic reading is 120 mmHg in one arm and 140 mmHg in the other, the difference is 20 mmHg. The first step is to repeat the measurements carefully. If a substantial difference persists, arrange a discussion with a healthcare professional. A single comparison is not enough to diagnose hypertension or identify the reason for the difference.
Could the cuff cause different readings?
Yes. A cuff that is too small or too large can affect accuracy. The upper arm should be measured and matched to the cuff's specified range. If you are unsure, read our blood pressure cuff-size guide. For a complete technique refresher, see how to measure blood pressure correctly at home.
Can you use a rechargeable home monitor to compare arms?
A suitable upper-arm monitor can be used for routine home measurements, provided the cuff fits and the device is used according to its instructions. The Spinegear AXD-808 rechargeable upper-arm monitor has a 22–42 cm cuff, USB-C rechargeable power, a backlit display, voice guidance and memory for two users with up to 99 readings each. These are verified product features, not a claim of NHS endorsement or a guarantee of diagnostic accuracy.
Do not rely on any single home measurement to diagnose a vascular condition. If you are concerned about a consistent difference between arms, a clinician can assess your results and determine whether further checks are appropriate.
What else can make home readings vary?
- Timing: blood pressure naturally fluctuates over the day.
- Recent activity: exercise, caffeine or smoking shortly before checking may influence a reading.
- Position: crossed legs, unsupported back or an arm below heart level can affect results.
- Cuff fit: the wrong cuff size or uneven positioning can distort readings.
- Movement and talking: both can interfere with an automatic measurement.
- Stress: feeling anxious about the result can itself change blood pressure.
See our guide to common blood pressure measurement mistakes for additional practical checks.
When should you seek medical advice?
Tell your GP or practice nurse if you repeatedly find a substantial difference between arms, or if your home readings are consistently above the range advised for you. Do not adjust prescribed blood-pressure medicine based on one reading or an arm-to-arm comparison.
If you experience sudden chest pain, stroke-like symptoms, severe breathlessness or other emergency symptoms, call 999. These symptoms need urgent assessment regardless of the numbers shown on a home monitor.
Frequently asked questions
Is a small difference between arms normal?
A small difference can occur, especially when measurements are taken at different times. What matters is whether a larger difference persists when readings are repeated carefully.
Does a difference of more than 15 mmHg mean an artery is blocked?
No. NICE uses that threshold to guide repeat measurements and which arm to use for subsequent checks. It does not establish a diagnosis or identify the cause of a difference.
Should I always use my left arm?
Not necessarily. NICE advises that when a difference above 15 mmHg persists on repeat measurement, subsequent readings should be taken in the arm with the higher result. Follow any individual advice from your clinician.
Can I check both arms with one cuff?
Yes, if the cuff fits both upper arms within its stated size range and you position it correctly each time. Follow the device instructions and allow time between readings.
Key takeaway
A one-off difference between arms is not a diagnosis. Measure carefully, repeat a difference above 15 mmHg, and use the higher-reading arm for future checks if that difference persists, in line with NICE guidance. Ask your healthcare professional about a persistent difference or worrying readings.
UK sources
This guide is for general information and is not a diagnosis or a substitute for individual medical advice.
