Thousands of people in Britain may be incorrectly told they have high blood pressure because of basic errors made during routine NHS checks, a GP has warned.
NHS advice states that patients should sit upright while having their blood pressure measured, with the arm comfortably supported on a table.
However, specialists say this procedure is not consistently followed in busy medical practices, potentially leading to misleading readings 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 side effects caused by medication can lead to genuine harm, especially among vulnerable patients.
“Using the wrong technique can ultimately lead to unsuitable treatment decisions and a poorer quality of life.”
His warning comes after a recent US study showed that the position of a person’s arm can make a “huge difference” to their blood pressure reading.
Researchers at Johns Hopkins Medicine found that allowing the arm to hang unsupported at the patient’s side raised systolic blood pressure—the top figure in a reading—by almost 7mmHg.
Experts warn that holding an arm at the side or resting it on the lap during a blood pressure check can make a “huge difference” to the result
Resting the arm on the lap also caused systolic pressure to be overestimated by nearly 4mmHg.
The researchers said the results support NHS guidance recommending that the arm be placed on a desk or table at heart level during a blood pressure check.
When the arm is left unsupported at the side, the muscles may tense, causing blood pressure to rise temporarily.
Placing the arm across the lap can also leave it further below the heart, which may increase the pressure recorded in the arm.
High blood pressure affects roughly one in three adults in England and can increase the risk of stroke, heart attack, kidney disease and dementia.
Because the condition usually produces no noticeable symptoms, many people do not realise they have it until serious damage has occurred.
More than four million people across England are thought to have high blood pressure without knowing it.
The findings, published in JAMA Internal Medicine, were released as the American Heart Association issued updated advice highlighting the importance of taking accurate readings when monitoring blood pressure at home.
Patients are advised to sit quietly for at least five minutes before the measurement, keeping both feet flat on the floor and their back supported. The centre of the adjustable cuff should be level with the heart, while the arm rests on a desk or table.
For the 2024 study, Johns Hopkins Medicine researchers recorded the blood pressure of 133 adults aged between 18 and 80.
Before their blood pressure was measured, participants walked for two minutes to replicate arriving at a doctor’s appointment, then sat down 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.