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Huge swathes of the UK population are missing out on hypertension treatment or taking drugs unnecessarily because of inaccuracies in equipment for measuring blood pressure, a new study reveals.

Study leader Professor Andrew Shennan, the Government's chief adviser on blood pressure measurement, warn-ed the phase-out of mercury sphygmomanometers was lea-ving GPs increasingly reliant on inaccurate devices.

The audit of equipment used in 45 London practices found over half of aneroid devices were out by 3mmHg or more ­ enough to misdiagnose a 'substantial proportion of the population'.

Professor Shennan, professor of obstetrics at King's College London, said: 'If you overestimate by 3mmHg you increase the number classified as hypertensive by 24 per cent. And if you underestimate by 3mmHg you cause 19 per cent misclassification.

'This has huge implications. People are on lifelong treatment when they don't need it or are not being treated. This translates into a lot of mortality ­ due to something simple like a blood pressure machine.'

Professor Shennan, who is chair of the Government's Committee on Blood Pressure Monitoring in Clinical Practice, said the potential for inaccuracies had not been properly considered when the decision to phase out mercury sphygmos was taken.

The study, published in Blood Pressure Monitoring this week, assessed 279 sphygmomanometers against an electronic reference pressure sensor and found 18 per cent of devices were out by more than 3mmHg.

Some 53 per cent of aneroid devices were out by over 3mmHg, compared with only 13 per cent of mercury devices and just 4.5 per cent of automated devices.

'A service model for improving blood pressure monitoring in primary care needs to take into account the proliferation of pressure scale errors, the lack of regular checks and the poor quality of some of the devices currently in use,' the researchers concluded.

Professor Shennan said it was essential to calibrate aneroid sphygmos at least once a year against mercury devices as 'even small errors misdiagnose a substantial proportion of the population'.

Fellow committee member Dr Peter McCartney, a GP in Bristol, said: 'Here is more

evidence of inaccurate basic equipment in daily use in the NHS.'

He singled out devices provided for promotional purposes by pharmaceutical companies for particular criticism and said they should be discarded. The study found 36 per cent of promotional aneroid devices were out by more than 5mmHg and 14 per cent by more than 10mmHg.

The Department of Health is to release new guidance on blood pressure measurement in the near future.

By Daile Pepper

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