Blood pressure measurements can vary between the upper extremities of healthy adults, and may be higher on the left than on the right, or on the right than on the left. Some people believe that the right upper extremity should be used for blood pressure measurement, which is not justified. Most people have similar blood pressure in both upper arms, with the difference generally not exceeding 10 mmHg. In patients with hypertension, the blood pressure of both upper extremities should be measured at the first visit. When bilateral blood pressure measurements differ, it is recommended that the blood pressure reading on the side with the higher blood pressure be used as the basis for diagnosis and efficacy assessment. If the difference in blood pressure measurements between the two sides exceeds 20 mmHg, attention should be paid to checking for significant narrowing of large vessels such as the subclavian artery on the side with the lower blood pressure (e.g., atherosclerotic lesions or multiple aortitis). There are many studies suggesting that hypertensive patients with a large difference in blood pressure between the two sides have a significantly higher chance of having a heart attack or brain attack, so this phenomenon should not be taken lightly.