Most people are right-handed, so the blood pressure of the right hand is usually higher than that of the left hand by 5-10 mmHg. Some patients with left-handedness may have a higher blood pressure in the left hand than in the right hand, but only by 5-10 mmHg. If the difference in blood pressure between the left and right hands exceeds 20 mmHg, it is important to pay attention to whether there is occlusion of the upper extremity blood vessels, more commonly occlusion or stenosis of the brachial or subclavian arteries. If the difference in blood pressure between the left and right hand is greater than 20 mmHg, ultrasound can be done to further clarify whether there is occlusion of the upper extremity vessels.