According to the June 2002 issue of the Journal of Hypertension, blood pressure should be measured in both arms on the first consultation. Most people are not aware that it is common for blood pressure readings to differ by as much as 10 points from arm to arm. Patients taking their own blood pressure should ask their doctors which arm to use from then on. (Most doctors will recommend using the arm with the higher reading.)
Patients can take their blood pressure at any time of the day, but they should be warned not to take it after smoking a cigarette or consuming a beverage containing caffeine or if they have a full bladder. The results are most accurate when patients are relaxed and sitting up for at least 5 minutes before slipping on the cuff or using a similar measuring device.