Why are blood pressure readings different in both arms?

Written by sara sentor
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The blood pressure in both arms may vary slightly, but the difference in a healthy individual should be negligible. A wide difference in the blood pressure readings of both arms suggests that there is a definite underlying problem.

Blood Pressure

Blood pressure is represented by two numbers. The top number is representative of the systolic pressure. Systolic pressure is the maximum pressure of blood from the heart. The lower number is the diastolic pressure, which is the amount of pressure between beats in the arteries. If the difference is more than 10mm Hg there may be a problem with the blood flow due to constricting arteries.

Normal Blood Pressure Difference

Health care providers will usually take your blood pressure in both arms and then choose the one that has the higher value. In every examination after that, blood pressure is taken from only the arm that gave the higher reading.

Morbidity and Mortality

According to research conducted by Andrew A. Skolnick (2002), a large difference in blood pressure (over 15mm Hg) between the arms is suggestive of increased morbidity and mortality. This difference may be caused due to peripheral vascular disease; the patient may be at risk of developing cardiovascular (heart problems) and cerebrovascular (e.g., hypertension) conditions.

Congenital Conditions

It is suggested that if your arms have a difference of 10mm Hg, then a number of readings should be taken for the next week. These should be taken after you have rested for at least 5 minutes. If after the week there is still a difference in readings of the two arms of at least 10mm Hg, then your physician will try to find out the cause of the difference. This difference may arise due to an underlying congenital condition like the thinning of the arteries in the arms or chest. Some other arterial conditions may be plaques or blood clots.


At times age may be responsible for the increase in blood pressure between the arms. There may be no other pathology present. In adults over the age of 50, there is usually a rise in the difference in blood pressure of the arms. However, the rise should never be taken as normal if it is over 15mm Hg.

Aortic Dissection

Another cause of a difference in blood pressure is an aortic dissection, commonly known as a tear inside the arterial wall. The correlation is small yet significant. Another significant cause of rise in blood pressure difference of both arms may be something called a subclavian steal. This is when the subclavian (chest) artery gets blocked, giving rise to a blood pressure difference of 20mm Hg or more.


In order to diagnose the condition, a contrast-enhanced CT of the chest should be done to negate any of the possible conditions. A vascular ultrasound may also help, but the CT would give a more detailed view.

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