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Measuring BP when patients are alone 'virtually eliminates' white coat hypertension

If patients are left alone when their blood pressure is measured, then automated devices can be used to virtually eliminate white-coat hypertension in a GP surgery, a new study reveals.

Readings taken automatically by a blood pressure monitor, with patients left alone in the room, were significantly lower than those taken manually.

This study was part of the conventional versus automated measurement of blood pressure in the office (CAMBO) trial.

Some 67 GP practices in eastern Canada were randomised to either use manual office blood pressure measurement – with a mercury or aneroid sphygmomanometer - or automated office blood pressure with a BpTRU device to monitor patients with known systolic hypertension.

The automated monitors take an initial ‘test' reading, and the patient is then left alone as a further five readings are automatically taken at two-minute intervals.

Initial results showed automated office readings were closer to awake ambulatory measurements than manual measurements, and the new study provides evidence of the persistence of this effect at two-year follow-up.

At the first routine clinic visit after study enrolment, mean systolic blood pressure fell by 14.3mmHg in 252 patients monitored automatically, compared with a drop of 8.0mmHg in 209 patients monitored manually.

Automated readings were 1.8mmHg higher than mean awake ambulatory measures taken at baseline, while manual measurements were 7.3mmHg higher. At two-year follow up, automated office readings decreased by 16.3mmHg, compared with 12.4mmHg with manual readings.

The decreases in blood pressure were attributed to participation in a research study changing the way blood pressure was monitored, rather than any specific intervention.

Study leader Professor Martin Myers, professor of medicine at the University of Toronto, said: ‘Although ambulatory blood pressure monitoring may be the ideal method for diagnosing hypertension, it is not always available and is impractical for following patients during repeated office visits. Automated office blood pressure virtually eliminates the white coat response'.

Dr Ivan Benett, a cardiology GPSI in Manchester said: ‘This paper seems to suggest automated blood pressure is virtually as good as the gold standard.'

Dr Terry McCormack, a GP in Whitby and member of the guideline development group for the 2011 NICE hypertension guidelines, said automated testing could be used to assess the need for full ambulatory blood pressure monitoring.

He said: ‘As it is fully automatic it does not need the presence of a health worker, and the patient is relaxed and rested. It could be used to decide who has a clinic BP greater than 140/90mmHg and  needs ambulatory blood pressure measurements.'

Family Practice, online first 24 November

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