Think you have high blood pressure? You might just be measuring it wrong

A doctor takes a patient's blood pressure
A doctor takes a patient's blood pressure

People could be being diagnosed with high blood pressure because they are holding their arms the wrong way during tests, research suggests.

Scientists found that arm position makes a “huge difference” to obtaining accurate readings.

Having an arm hanging by the side during the test, rather than placed on a desk, created the greatest distortion, substantially inflating the numbers.

But resting an arm on the lap also meant readings were significantly raised.

Researchers in the United States found that leaving the arm unsupported and hanging at the patient’s side overestimated systolic pressure (the top number in a blood pressure reading) by 6.5mmHg and diastolic blood pressure (the bottom number) by 4.4 mmHg.

Putting an arm on the lap saw systolic pressure overestimated by 3.9mmHg and diastolic blood pressure by 4mmHg.

The NHS advises that the right way to have a reading taken is to sit on an upright chair with a back, placing both feet flat on the floor and resting the arm on a table or desk.

Patients are also advised to rest for five minutes before taking a reading and then take another reading several minutes later to check that it is accurate.

High blood pressure increases the risk of heart attacks and strokes, as well as diseases such as vascular dementia, but because it has no symptoms, it is impossible to detect without being tested.

An estimated 4.2 million people in England have the condition without knowing it.

The findings from researchers at Johns Hopkins Medicine in the US were published in the journal JAMA Internal Medicine.

Dr Tammy Brady, from the Johns Hopkins University School of Medicine, said that arm position makes a “huge difference” when it comes to an accurate blood pressure measurement and that people should always have their arm on firm support such as a desk or table.

For the study, researchers recruited 133 adults aged 18 to 80, whose blood pressure was taken during a single visit.

Before readings were taken, all those in the study emptied their bladders, walked for two minutes to replicate somebody coming to the clinic, and then sat down and rested for five minutes with their backs and feet supported.

Each person wore an upper arm blood pressure cuff that fitted their arm and had a series of measurements taken with a digital blood pressure device 30 seconds apart.

The results suggested people could end up having high blood pressure readings simply based on the position of their arm, with an arm hanging by the side offering the highest readings.

The NHS advises that normal blood pressure is between 90/60mmHg and 120/80mmHg.

High blood pressure is considered to be 135/85 or higher if the reading was taken at home, or 140/90mmHg or higher if the reading was taken at a pharmacy, GP surgery or clinic.

The NHS is rolling out blood pressure checks in workplaces and at dentists’ surgeries and opticians practices in a bid to catch more cases earlier.

The schemes are part of efforts to find the more than four million people suffering from the “silent killer”.