Did YOUR doctor measure your blood pressure incorrectly? A major error distorts the results, experts discover

If you have been diagnosed with high blood pressure, it may be worth asking the doctor to check it again.

The incorrect arm position has been linked to much higher readings than when carried out in the way the NHS recommends: sitting in an upright chair, resting on a table or desk.

Other positions, such as resting the arm on the lap or to the side, can significantly overestimate blood pressure readings, researchers found.

Experts suggest it can make a ‘big difference’ and potentially lead to misdiagnoses, highlighting the need for a universal approach to the measurements.

The incorrect arm position has been linked to much higher readings than when carried out in the way the NHS recommends: sitting in an upright chair, resting on a table or desk

Researchers from Johns Hopkins Medicine in the US recruited 133 adults aged 18 to 80, whose blood pressure was measured during one visit.

Before measurements were taken, all study participants emptied their bladders, walked for two minutes to mimic someone coming to the clinic, and then sat down and rested with their back and feet supported for five minutes.

Each subject wore an upper arm blood pressure cuff that fit around the arm, and a series of measurements were taken with a digital blood pressure device at 30-second intervals.

They took measurements when the arms were supported on a desk, the arms on their lap, and when the arms were unsupported and hanging at the patient’s side.

Placing an arm on your lap was found to overestimate systolic pressure (the top number that represents the pressure as your heart pushes blood out) by 3.9 mmHg.

It also increased diastolic blood pressure – the bottom number that measures pressure while your heart is resting – by 4mmHg.

Meanwhile, an unsupported arm hanging to the side overestimated systolic pressure by 6.5 mmHg and diastolic by 4.4 mmHg.

The findings, published in the journal JAMA Internal Medicine, suggest that people may end up with high blood pressure readings simply based on the position of their arm, with an arm hanging to the side producing the highest readings.

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

High blood pressure is considered to be 135/85 or higher if the measurement is taken at home.

If the measurement was taken in a pharmacy, GP practice or clinic, the figure will be 140/90 mmHg or higher.

The authors recommend that people rest for five minutes before taking a first measurement, and then take a second measurement after a few minutes to check whether the reading is correct.

Lead researcher Dr Tammy Brady said the different arm positions were often used in clinical practice, perhaps because doctors were not aware of these differences.

She said: ‘This level of blood pressure error could lead to a significant number of people being overdiagnosed with hypertension.’

Professor Bryan Williams, chief scientific officer and medical director at the British Heart Foundation, added: ‘This study reinforces why guidelines are very specific about how blood pressure should be measured to ensure readings are accurate.

‘Measuring blood pressure is one of the simplest ways to identify people at risk of heart disease or stroke, but it is important that the measurement is taken correctly if it is to be used to guide treatment decisions.’