Thousands of Britons could be wrongly diagnosed with high blood pressure because of simple mistakes during routine NHS checks, a GP has warned.
NHS guidance advises patients to sit upright with their arm supported on a table when readings are taken.
But experts warned the recommendation is not always followed in busy clinics, raising the risk of inaccurate results and incorrect diagnoses.
‘Accurate blood pressure measurement is essential if we are to correctly identify and treat people at risk of damage from high blood pressure,’ Dr Dean Eggitt, an NHS GP, told the Daily Mail.
‘Over-treatment and medication-induced side effects can cause real harm, particularly in vulnerable patients.
‘Poor technique can ultimately result in inappropriate treatment decisions and reduce quality of life.’
The warning follows a recent US study that found arm position makes a ‘huge difference’ to blood pressure readings.
Experts at Johns Hopkins Medicine found that allowing an arm to hang unsupported by a patient’s side increased systolic blood pressure – the top number in a reading – by nearly 7 mmHg.
Holding an arm by your side or on your lap during a reading can make ‘huge difference’ to blood pressure readings, experts warn
Resting the arm in the lap also saw this number overestimated by almost 4mmHg.
Experts say the findings reinforce NHS guidance which calls for a patient’s arm to be placed on a table or desk at heart level when their blood pressure is checked.
This is because when the arm is left hanging, muscles can contract, temporarily raising blood pressure.
Placing the arm in a patients lap, meanwhile, can create a larger distance between the arm and the heart, increasing blood pressure in the arm.
High blood pressure – which affects around one in three adults in England – increases the risk of stroke, heart attack, kidney disease and even dementia.
But because it rarely causes symptoms, it often goes undetected until it is too late.
More than four million people in England have the condition without knowing it.
The findings – published in the journal JAMA Internal Medicine – came amid updated guidance from the American Heart Association which places greater emphasis on accurate blood pressure measurement when monitoring the problem at home.
Patients are also advised to sit quietly for at least five minutes before a reading is taken, with both feet flat on the floor and their back supported. The middle of an adjustable cuff should be at mid-heart level while the arm rests on a desk or table.
For their 2024 study, researchers from Johns Hopkins Medicine measured the blood pressure of 133 adults aged 18 to 80 years old.
Before readings were taken, all participants walked for two minutes – as if they had just arrived at a doctor’s appointment – before sitting for five minutes.
Participants were fitted with an upper arm blood pressure cuff and underwent a series of measurements, 30 seconds apart.
The results suggested patients could end up being diagnosed with high blood pressure – medically known as hypertension – simply based on the position of their arm, with leaving the arm hanging by the side returning the highest readings.
Researchers found this arm position overestimated systolic pressure by 6.5mmHg and diastolic pressure by 4.4mmHg.
The researchers said the differences were large enough to affect whether some patients met the threshold for a diagnosis of hypertension.
According to the NHS, a normal blood pressure is between 90/60mmHg and 120/80mmHg.
High blood pressure is considered anything over 135/85mmHg if the reading was taken at home and 140/90mmHg or higher if it was taken by a healthcare professional at a pharmacy, GP surgery or hospital.
The warning comes after separate analysis by researchers at the University of Oxford suggested more than half of people living with high blood pressure are unaware they have it – leaving them at increased risk of early death.
The researchers also estimated only half of those being treated for the condition by their GP have their blood pressure under control.
The authors said current guidelines from the National Institute for Health and Care Excellence (NICE) mean many with high blood pressure are never picked up, treated or go on to have good blood pressure control.
They argued that current diagnostic pathways can create a ‘leaky cascade of care’, with some patients never receiving a diagnosis or effective treatment.
