Normally blood pressure difference in arms is not a big problem, provided pressure difference is of small value.

Generally we divid blood pressure values in two parts. When heart contracts blood pressure in vessels is called as systolic, and when heart relaxes blood pressure in arteries is named as diastolic. A difference of less than 5 millimeters of mercury (mm Hg) between arms for either reading is normal. However, a difference of more than 20 mm Hg for systolic pressure or more than 10 mm Hg for diastolic pressure may be a sign of an underlying problem — such as narrowing of the main arteries to that arm or co-arctation of Aorta, or aortic dissection. If you have a significant difference in blood pressure readings between both arms, consult your doctor for an evaluation. Your doctor may go for chest X-ray, echocardiography or doppler studies of arteries of your arm.

Many factors may affect your blood pressure. To know a difference in blood pressure between both arms, your doctor may take a series of alternate-arm blood pressure readings. He or she may also take your blood pressure in both arms at the same time with two blood pressure gauges and two observers. If your blood pressure is high in one arm than the other, then blood pressure at high side is considered as actual blood pressure and treat that pressure.