Blood pressure (low) - Diagnosing low blood pressure

Low blood pressure (hypotension) can be easily diagnosed by measuring your blood pressure.

A blood pressure reading is taken using two measurements. The first is known as systolic, which is the pressure in your arteries when your heart contracts and pushes blood around your body.

The second measurement is known as diastolic, which is the pressure in your arteries when your heart refills with blood in between heartbeats. Both systolic and diastolic blood pressures are measured in millimetres of mercury (mmHg).

How blood pressure is measured

Blood pressure is often measured using a sphygmomanometer, a device which consists of a stethoscope, arm cuff, dial, pump and valve.

The cuff is placed around your arm and pumped up to restrict the blood flow. The pressure is then slowly released as your pulse is checked using the stethoscope.

Hearing how your pulse beats after the cuff is released allows a measurement to be taken on the mercury scale, giving an accurate reading of your blood pressure.

Many GP surgeries now use digital sphygmomanometers, which measure your pulse using electrical sensors.

Before having your blood pressure taken, you should rest for at least five minutes and empty your bladder.

To get an accurate blood pressure reading, you should be sitting down and not talking when the reading is taken.

After you have had your blood pressure taken, your GP or nurse will give you your systolic reading first followed by your diastolic reading. If your systolic blood pressure is 120 mmHg, and your diastolic blood pressure is 80 mmHg, you will be told that your blood pressure is 120 over 80, written as 120/80.

Low blood pressure

As a general guide, low blood pressure is a reading below 90/60. 

If you have low blood pressure according to this guide, you do not need to worry. Naturally low blood pressure rarely causes symptoms or needs treating. Having low blood pressure is considered healthy because it protects you from the risks and diseases of high blood pressure.

Postural or orthostatic hypotension

If your symptoms of low blood pressure mostly occur when you change position (postural or orthostatic hypotension), your blood pressure may be measured before and after you move. For example, your blood pressure may be measured while you are sitting down and again while you are standing up.

Depending on what your seated blood pressure is, if your systolic reading falls by between 15 to 30 mmHg when you stand up, you may have orthostatic hypotension.

Identifying underlying causes

Your GP or practice nurse will usually be able to diagnose low blood pressure very easily. However, determining the reason for low blood pressure can often be more difficult.

If you have an underlying condition causing low blood pressure, it is likely you will have other symptoms as well. You should discuss these with your GP, who may recommend further tests.

Further tests may include blood tests to check for anaemia and measurements taken of your hormone levels or blood sugar (glucose) level, or an electrocardiogram (ECG) to detect any irregularities in your heart rhythm.