There is a normal difference in measuring blood pressure, and the left upper arm may be different from the right upper arm. Should I measure my blood pressure with the left upper arm or the right upper arm? Some say the left upper arm, some say the right upper arm, and some choose whoever is taller. So which arm do you choose? Today we will discuss this issue with you in the context of the Chinese Blood Pressure Measurement Guidelines 2011. Normal people generally have higher blood pressure in the right upper limb than in the left upper limb, with a difference of 5-10 mmHg, which is determined by the anatomy and physiology of the blood vessels. This is because the right brachial artery comes from a branch of the cephalic trunk and the left brachial artery comes from the left subclavian artery. Both the cephalic trunk and the left subclavian artery come from the aorta, and the cephalic trunk is a larger branch of the aorta, while the left subclavian artery branch is smaller, so the blood pressure on the right side is naturally higher. This is why right-handed blood pressure is currently predominant in clinical practice. However, there are many people who have higher blood pressure in the left upper arm. Many studies have found a difference in blood pressure between the left and right upper arms, and this difference is not related to the use of the left or right hand. The difference in blood pressure between arms in hypertensive patients is ≥5 mmHg in 31% of cases, and the proportion of cases in which blood pressure is higher on one side of the left and right upper arms than on the opposite side is comparable (i.e., the proportion of cases in which blood pressure is higher in the left upper arm than in the right upper arm is approximately 50% as compared to the proportion of cases in which blood pressure is higher in the right upper arm than in the left upper arm). Therefore, the guidelines recommend that left and right upper arm blood pressure should be measured at the first examination. When the blood pressure in the right and left upper arms is not the same, the blood pressure measured in the arm with the higher value is used. Therefore, if you are having your blood pressure measured for the first time, you can choose to have your blood pressure measured on both the left and right upper arm to determine which arm has the higher blood pressure. The side with the higher blood pressure is used as the upper arm for blood pressure measurement. Generally, after a person forms a difference in blood pressure between the left and right arm, the direction will not change for a period of time, so the next time we measure it, the higher blood pressure will prevail in one hand. For example, if the left hand is the standard, then the left hand will be measured every time. However, the difference may change over a longer period of time. Therefore, it is necessary to measure again periodically whether the direction of the difference between the left and right hand blood pressure has changed. In healthy individuals, there can be a difference of 5-10 mmHg between the blood pressure of the two upper extremities, but if the difference between the arms persists >20 mmHg, it is highly suggestive of vascular disease such as narrowing of the aortic arch and occlusion of the arteries in the upper extremities. The elderly and patients with diabetes mellitus or certain diseases are prone to postural hypotension and it is recommended to measure blood pressure in multiple positions. If needed, blood pressure can be measured in the prone or standing position. Standing blood pressure measurement should be performed 3 minutes after changing from prone to standing.