You should measure blood pressure in both arms at least once, then use the arm with the higher reading for all future measurements. This has been the standard recommendation from hypertension guidelines in the U.S., Europe, UK, and Canada for decades. The reason is simple: if one arm consistently reads lower, it could be masking your true blood pressure or signaling a vascular problem.
Why Both Arms Matter at First
A small difference between arms is completely normal. Most people have a gap of less than 5 mmHg between their left and right arm, which is nothing to worry about. But some people have a much larger gap, and the only way to find out is to check both sides.
The American Heart Association recommends measuring both arms during an initial blood pressure assessment. Once you know which arm reads higher, that becomes your go-to arm for home monitoring and clinic visits, unless your doctor says otherwise. The higher-reading arm gives a more accurate picture of the pressure your heart and blood vessels are actually dealing with. Using the lower arm could lead you to underestimate your blood pressure and miss early hypertension.
When a Big Difference Between Arms Is a Warning Sign
A persistent difference of 10 mmHg or more in the top number (systolic pressure) between your arms is considered clinically meaningful. A gap of 15 mmHg or more is a stronger red flag. These differences don’t just affect which number you track. They can point to real cardiovascular problems.
A meta-analysis published in The Lancet found that a difference of 15 mmHg or more between arms was associated with 2.5 times the risk of peripheral vascular disease, 1.6 times the risk of pre-existing cerebrovascular disease, and a 70% increase in the risk of dying from cardiovascular causes. Even a 10 mmHg gap was linked to more than double the risk of peripheral vascular disease.
The most common reason for a large inter-arm difference is subclavian artery stenosis, a narrowing of the artery that supplies blood to your arm. This narrowing is typically caused by plaque buildup, the same process behind heart attacks and strokes. The arm with the lower reading is the one with reduced blood flow. So if your doctor discovers a significant gap, they may want to investigate your arteries more closely.
Arms You Should Never Use
Certain medical conditions make one arm off-limits for blood pressure cuffs entirely:
- Dialysis fistula or graft. If you have an arteriovenous fistula for kidney dialysis, no one should take blood pressure or draw blood from that arm. The pressure from a cuff can damage the fistula.
- Mastectomy or lymph node removal. After breast cancer surgery involving lymph node removal or biopsy, the arm on the surgical side should be avoided for blood pressure, IVs, and blood draws when possible. This helps protect against lymphedema, a painful swelling caused by disrupted lymph drainage. If both arms are restricted (for instance, after bilateral surgery), your care team will determine the safest option.
- PICC lines or deep vein thrombosis. An arm with a central catheter or an active blood clot should not be used for blood pressure measurement.
If any of these apply to you, your available arm becomes your default regardless of which one reads higher.
How to Check Both Arms at Home
If you’ve never compared your arms, you can do it yourself with a home blood pressure monitor. Sit quietly for five minutes, then take a reading on one arm. Wait one to two minutes, then switch the cuff to the other arm and take another reading. Repeat this a couple of times on different days to see if a consistent pattern emerges. If one arm is consistently 10 or more points higher on the top number, mention it to your doctor.
Once you’ve identified your measurement arm, stick with it every time. Switching between arms introduces variability that makes it harder to spot real trends in your readings over time.
Getting an Accurate Reading Every Time
Which arm you use matters, but so does how you position it. Poor technique can skew your numbers by 10 mmHg or more, enough to change whether your reading looks normal or elevated.
Keep your arm at heart level during the measurement. If you’re sitting, rest your arm on a table, desk, or pillow so the cuff sits roughly even with your chest. If you’re standing, let your arm hang relaxed at your side or support it with your other hand at chest height. Don’t hold your arm up unsupported, because the muscle tension alone will raise your reading.
Stay still and quiet while the cuff inflates and deflates. Don’t talk, scroll your phone, or cross your legs. Keep your arm relaxed rather than tensed or clenched. Sit with your back supported and your feet flat on the floor. These details sound minor, but they add up. A reading taken with your arm dangling below heart level, for example, can read artificially high simply because of gravity’s effect on blood flow.
For the most reliable tracking, measure at the same time of day, on the same arm, in the same position. Blood pressure naturally fluctuates throughout the day, so consistency in your routine helps you and your doctor distinguish real changes from normal variation.