Significant differences in blood pressure between the RUE and the LUE (left upper extremity) may be due to a condition called coarctation of the aorta
- which is a condition you have had your entire life. If this difference in blood pressure between the RUE and the LUE is new (other than something you just didn't notice before), there are several other things that come to mind - without more medical history, I would just be purely guessing.
Regardless it is worthwhile to have this finding further evaluated, even if you have no known symptoms. Discuss it first with your primary doctor who can verify the differences and order tests and/or provide a referral to the appropriate specialist if he/she feels it is warranted.