a small difference in blood pressure readings between arms isn’t a health concern. However, a difference of more than 10 millimeters of mercury (mm Hg) for either your systolic pressure (top number) or diastolic pressure (bottom number) may be a sign of an underlying problem — such as narrowing of the main arteries to that arm. If you have a significant difference in blood pressure readings between arms, talk to your doctor.
A difference of 10 to 15 mm Hg for systolic pressure that shows up repeatedly is a risk factor for vascular disease and for a greater risk of developing cardiovascular disease and related complications during the next 10 years.
Your doctor may measure your blood pressure in both arms to see if you have high blood pressure (hypertension). If your blood pressure is higher in one arm, your doctor will probably use the blood pressure reading from that arm to monitor your blood pressure
A large difference in blood pressure measurement between your arms could signal a health problem, such as:
Blocked arteries in your arms (peripheral artery disease) Kidney disease Diabetes Heart defects