You should have your blood pressure measured in both arms, at least at your initial visit to a health care provider. In many people the readings will differ slightly, which is normal.
If the difference is big (more than 10 points in systolic pressure, the first number), the measurement should be repeated; if it persists, a medical evaluation should be done to determine the underlying cause. A large inter-arm systolic difference may be an indication of increased cardiovascular risk, as was confirmed by an analysis of people in the Framingham Heart Study, published recently in the American Journal of Medicine.
Those with a large inter-arm difference were more likely to have diabetes, hypertension and undesirable cholesterol levels, but even when the researchers controlled for such factors, inter-arm difference was still linked to increased risk.