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Study warns of widespread errors in BP readings after finding inter-arm variation in a fifth of patients

Arm variation distorts BP readings

By Lilian Anekwe

A substantial proportion of blood pressure measurements taken by GPs may be inaccurate because of inter-arm variations in readings, researchers warn.

A new systematic review found that as many as 20 per cent of patients had clinically significant inter-arm differences in blood pressure.

Patients with hypertension were particularly likely to

have inter-arm differences, suggesting there could be an important impact on diagnosis.

The researchers argued current hypertension guidelines failed to sufficiently emphasise the importance of inter-arm variation.

Their review of four studies estimated 19.6 per cent of patients had an inter-arm difference in systolic blood pressure of 10mmHg or more.

Some 51 per cent of patients with hypertension had inter-arm differences in systolic blood pressure of more than 20mmHg.

'Given this estimate, there is a one in 10 risk that a blood pressure measurement could be underestimated by more than 10mmHg if inter-arm difference is not accounted for,' the researchers wrote.

Inter-arm difference 'needs to be looked for in all patients whose diagnosis and treatment depend on accurate blood pressure measurements,' they add-ed in December's Journal of Human Hypertension.

Study leader Dr Christopher Clark, a clinical academic fellow at the Peninsular medical school and a GP in Witheridge, Devon, said: 'The guidelines stop short of letting GPs know this is quite a common problem of which we should be on our guard.

'It's common enough that GPs should check both arms systematically in patients in whom blood pressure measurements are advisable.'

But other GPs described the implications as either unworkable or unclear.

Dr Andreas Arvanitis, a GP in Cleveleys, Lancashire, and cardiac lead for Wyre PCT, said: 'There is not enough time to take measurements twice in each arm. I don't think it's possible in the real world.'

Dr Kathryn Griffiths, a GP in York and clinical CHD lead for Selby and York PCT, said the research did not establish which arm had higher blood pressure – with readings normally taken in the right.

'This research possibly asks more questions than it answers. If there is a difference, then the important thing is to be consistent in how measurements are taken,' she said.

Getting it wrong on hypertension

• White coat hypertension – around 15 to 20 per cent of patients diagnosed with hypertension have normal blood pressure at home

• Number of measurements – short-term fluctuations can mask longer-term problems

• Measurement site – blood pressure measured at arm

may not reflect blood pressure at heart

• Arm position – blood pressure measured with the arm perpendicular to the body lower than with the arm in a parallel position

• Choice of arm – new research finds a fifth of patients have significant inter-arm variation

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