Difference in Blood Pressure Between Arms: Causes and Risks

A persistent difference in systolic blood pressure of 10 mmHg or more between your arms is a warning sign of underlying vascular disease, and at 15 mmHg or more it is linked to a meaningfully higher risk of dying from cardiovascular causes. Most people have a small gap between arms, often just a few millimeters of mercury, which is harmless. But larger, reproducible differences point to narrowed arteries, sometimes in locations you would never feel until something goes seriously wrong. The tricky part is that how the measurement is taken, and who is being measured, changes both the numbers and what they mean.

How Common Are These Differences

Almost everyone has some measurable difference in blood pressure between their left and right arms. In a large study of more than 134,000 people in Indian primary care, the average gap in systolic blood pressure between arms was trivially small, less than 1 mmHg. But when researchers looked for clinically meaningful gaps, about 5.8% had a systolic difference between 10 and 15 mmHg, and roughly 2.2% had a difference of 15 mmHg or more.¹ In a smaller UK primary care study, the proportion was higher: about 24% of participants showed a systolic difference of 10 mmHg or more, and 9% reached 15 mmHg or more.² The wide range across studies partly reflects differences in the populations studied and how measurements were taken, a detail that turns out to matter a lot.

Why the Way You Measure Changes the Results

If a nurse checks one arm, removes the cuff, walks around, then checks the other arm a couple of minutes later, the difference will tend to look bigger than it actually is. Blood pressure naturally fluctuates from moment to moment, and the time gap between sequential readings introduces noise. A meta-analysis found that measuring sequentially more than doubled the chance of finding a systolic difference of 10 mmHg or more compared with measuring both arms at the same time.³ For the largest differences, the inflation was even more dramatic: the risk of seeing a 20 mmHg gap was nearly five times higher with sequential readings.

Studies using simultaneous dual-cuff devices consistently report smaller average differences. One head-to-head comparison found that the mean absolute systolic gap shrank from about 7.8 mmHg with sequential measurement to 6.2 mmHg with simultaneous measurement.⁴ This matters for you as a patient because a one-time sequential reading that shows a 12 mmHg gap might not represent a real vascular problem. If your doctor finds a meaningful difference, repeating the measurement with both cuffs inflating together, or at least repeating it on another day, gives a much more reliable picture.

The Most Common Vascular Cause

When a large, reproducible inter-arm difference does turn out to reflect disease, the most frequent culprit is narrowing or blockage of the subclavian artery, the large vessel that branches off the aorta and feeds blood to each arm. A narrowing on one side reduces pressure downstream, so the cuff on that arm reads lower. A meta-analysis in The Lancet found that among patients who underwent angiography, those with proven subclavian stenosis (more than 50% blockage) had an average systolic difference between arms of about 37 mmHg. A systolic difference of 10 mmHg or more was strongly associated with subclavian stenosis, with a risk ratio of roughly 8.8.⁵

Subclavian stenosis itself is usually caused by atherosclerosis, the same buildup of fatty plaque that narrows coronary arteries and leg arteries. So finding it in the subclavian artery is rarely an isolated problem. It tends to be a marker that atherosclerosis is widespread, which is why the inter-arm difference predicts trouble far beyond the arm. In one reported case, a patient had a right arm reading of 138/80 and a left arm reading of just 84/50. Imaging revealed total occlusion of the proximal left subclavian artery.⁶ That is an extreme example, but it illustrates how dramatically one blocked vessel can skew the numbers.

Subclavian Steal Syndrome

When subclavian narrowing gets severe enough, blood can actually reverse direction in the vertebral artery on that side. Normally, the vertebral artery carries blood upward to the brain. But if the subclavian is blocked upstream of where the vertebral branches off, the arm’s demand for blood “steals” flow backward through the vertebral artery, pulling it away from the brain’s posterior circulation.⁷ This is called subclavian steal syndrome, and it can cause dizziness, visual changes, or even fainting, especially when you exercise the affected arm.⁸ Many people with the reversed flow pattern have no symptoms at all, but when symptoms do appear, the inter-arm blood pressure gap is often the first measurable clue.

When the Difference Signals an Emergency

Aortic dissection, a tear in the wall of the aorta, is one scenario where a sudden, large inter-arm difference demands immediate attention. As the tear extends, it can obstruct blood flow to one of the subclavian arteries, causing an abrupt drop in pressure on that side. In emergency department studies, a systolic difference of more than 20 mmHg between arms was significantly associated with acute aortic dissection, with an odds ratio of about 2.7.⁹ A separate study found that a systolic inter-arm gap of 10 mmHg or more had roughly 62% sensitivity and 89% specificity for detecting acute dissection.¹⁰

The context matters enormously here. A chronic 12 mmHg difference in someone who has been measured several times is a completely different situation from a new 12 mmHg difference in someone who just arrived at the ER with tearing chest pain radiating to the back. The inter-arm gap is one piece of a diagnostic puzzle, not a standalone test, but in the right clinical setting it helps emergency physicians move faster toward imaging.

Inflammatory Artery Disease

Atherosclerosis is not the only thing that narrows arteries. Takayasu arteritis, a form of vasculitis that primarily affects the aorta and its major branches, can produce dramatic inter-arm differences, especially in younger patients. In a reported case of a 16-year-old girl, the right arm blood pressure was markedly higher than the left, and imaging revealed a thickened aortic wall plus complete occlusion of the left common carotid and left subclavian arteries.¹¹ A systolic difference of more than 10 mmHg between arms is, in fact, one of the six classification criteria used to diagnose Takayasu arteritis, alongside features like absent pulses, arterial bruits, and onset before age 40.¹²

Takayasu arteritis is rare, but it is worth knowing about because it strikes a younger population than typical atherosclerosis. A large inter-arm difference in a person under 40, especially if accompanied by fatigue, joint pain, or absent pulses, should prompt evaluation for vasculitis rather than just garden-variety plaque buildup.

What the Gap Predicts About Long-Term Survival

Several meta-analyses have pooled data across cohort studies to quantify the long-term risk attached to inter-arm differences. The overall picture is consistent: a systolic gap of 15 mmHg or more is associated with roughly 60% to 70% higher risk of cardiovascular death and all-cause death. The Lancet meta-analysis reported a hazard ratio of 1.7 for cardiovascular mortality and 1.6 for all-cause mortality at the 15 mmHg threshold.⁵ A later meta-analysis found broadly similar numbers, with a pooled hazard ratio for all-cause death of about 1.46 at the 15 mmHg cutoff and 1.53 at the 10 mmHg cutoff.¹³

There is some debate about whether the 10 mmHg threshold carries independent risk when you measure both arms simultaneously. A more recent meta-analysis that restricted itself to simultaneously measured readings found that a difference of 15 mmHg or more predicted increased all-cause mortality (hazard ratio 1.28), but the association at 10 mmHg fell short of statistical significance once the measurement method was controlled for.¹⁴ The practical takeaway is that 15 mmHg is the more robust red flag, while a difference in the 10 to 14 mmHg range deserves attention and repeat measurement rather than immediate alarm.

The UK primary care cohort mentioned earlier found even steeper risk: participants with a systolic difference of 10 mmHg or more had an adjusted hazard ratio for all-cause mortality of 3.6 over the follow-up period.² That number is higher than most meta-analytic estimates, likely because the study population was older and already in primary care, meaning the baseline risk was elevated. Single studies can overstate or understate the picture, which is why the pooled analyses from multiple cohorts provide a more stable estimate.

Peripheral Vascular Disease and the Inter-Arm Gap

Because subclavian narrowing usually reflects widespread atherosclerosis, an inter-arm difference often appears alongside peripheral arterial disease in the legs. In a study that directly compared patients with and without confirmed peripheral arterial disease, the average systolic inter-arm gap was about 10 mmHg in those with disease, compared with about 7 mmHg in those without. Among the peripheral arterial disease group, roughly a third had a gap exceeding 10 mmHg and about 18% exceeded 15 mmHg, rates far higher than in the non-diseased group.¹⁵ The Lancet meta-analysis similarly found that a 15 mmHg or greater difference carried a risk ratio of 2.5 for peripheral vascular disease and 1.6 for pre-existing cerebrovascular disease.⁵

This link matters practically. If your arms show a persistent gap, your doctor may want to check blood flow in your legs and neck arteries too, even if your only complaint was a funny blood pressure reading.

Which Arm’s Reading Should You Trust

When the two arms disagree, you might wonder which number is “your real blood pressure.” Guidelines generally recommend using the higher reading for managing hypertension, because the lower arm’s reading is being artificially depressed by the vascular obstruction. A large individual-participant meta-analysis confirmed that models based on the higher arm’s systolic reading were better at predicting all-cause mortality, cardiovascular death, and cardiovascular events than models based on the lower arm.¹⁶ The practical consequence is that if you only ever measure the lower arm, you might think your blood pressure is well controlled when it is not.

The Indian primary care study illustrates this problem vividly. Among participants with a systolic inter-arm difference of 15 mmHg or more, about 19% had blood pressure above 140/90 on one arm only. Had only the low arm been checked, those patients would have been classified as normotensive and potentially left untreated.¹ Checking both arms at least once establishes which arm reads higher, and that arm should be used for all future monitoring.

Why People with Diabetes Should Pay Extra Attention

Diabetes accelerates atherosclerosis throughout the body, and inter-arm differences show up more often and carry heavier consequences in people with the condition. A cohort study found that about 8.6% of people with diabetes had a systolic difference of 10 mmHg or more, compared with 2.9% of non-diabetic controls. In the diabetes group, a gap of 10 mmHg or more was associated with roughly 3.4 times the odds of peripheral arterial disease. At the 15 mmHg threshold, the associations were even starker: roughly 5.7 times the odds of diabetic retinopathy and 7 times the odds of chronic kidney disease. Looking forward over time, cardiovascular mortality was about 3.5 times higher with a 10 mmHg gap and 9 times higher with a 15 mmHg gap in the diabetes cohort.¹⁷

A cross-sectional study of people with type 2 diabetes in Palestine found a strikingly high prevalence of systolic inter-arm differences of 15 mmHg or more, at about 27.5%, and 30% of the same group had chronic kidney disease.¹⁸ The high rate in that particular population may reflect limited access to vascular screening and treatment, but the broader point holds: diabetes compounds the risk behind an inter-arm gap, making routine bilateral measurement more valuable in this group than in the general population.

Small Differences and the Dominant Hand

Not every inter-arm gap is a disease signal. Even in young, healthy people, small differences crop up for benign reasons. A study of more than 3,200 healthy young adults found that the dominant hand’s arm tended to have slightly higher blood pressure than the non-dominant arm. The researchers attributed this to greater muscle mass and arm circumference on the dominant side.¹⁹ A study of college freshmen found that right-handed students had an average systolic reading of about 119 mmHg in the right arm versus 118 mmHg in the left, and arm circumference was modestly larger on the dominant side.²⁰ These differences are in the range of 1 to 2 mmHg, well within normal variation and nowhere near the thresholds that predict vascular disease.

Another less-discussed source of temporary difference is simple anxiety or discomfort. If one arm was measured first and the patient was nervous, that reading may run a few points higher than the second arm. This is sometimes called a “white coat order effect,” and it is one more reason simultaneous measurement gives truer results. A veteran’s hospital study found that the arm measured first (consistently the right arm) read about 5 mmHg higher on average, but a week later the gap had shrunk by nearly half, suggesting that part of the initial difference was a transient artifact rather than a fixed vascular problem.²¹ That same study still found that reproducible differences carried prognostic weight: every 10 mmHg of persistent systolic inter-arm difference was linked to a mortality hazard ratio of about 1.24 after adjustment.

When to Investigate Further

Clinicians generally agree that a marked and persistent inter-arm disparity warrants investigation for occlusive arterial disease.²² “Persistent” is the key word. A single visit finding a 12 mmHg gap does not, by itself, mean anything is wrong. You could have been sitting at an angle, the cuffs might have been different sizes, or natural fluctuation could explain it. But if the gap shows up again on a second visit, especially with simultaneous measurement, further evaluation is reasonable. That usually starts with duplex ultrasound of the subclavian and carotid arteries and may include an ankle-brachial index to assess leg circulation. In younger patients with suggestive symptoms, blood work for inflammatory markers and CT angiography can help rule out vasculitis like Takayasu arteritis.

For home monitoring, inexpensive automated cuffs are widely available but almost nobody owns two of them. If you have been told you have an inter-arm difference, measure consistently on the arm your doctor identifies as the higher-reading side. That way your home readings track the number that best reflects your actual cardiovascular risk, rather than the artificially lowered number from the obstructed side.