Association of a difference in systolic blood pressure between arms with vascular disease and mortality: a systematic review and meta-analysis

So get your blood pressure checked in both arms.
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2811%2961710-8/fulltext

Background

Differences in systolic blood pressure (SBP) of 10 mm Hg or more or 15 mm Hg or more between arms have been associated with peripheral vascular disease and attributed to subclavian stenosis. We investigated whether an association exists between this difference and central or peripheral vascular disease, and mortality.

Interpretation

A difference in SBP of 10 mm Hg or more, or of 15 mm Hg or more, between arms might help to identify patients who need further vascular assessment. A difference of 15 mm Hg or more could be a useful indicator of risk of vascular disease and death.