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Blood pressure testing is misleading GPs

By Lilian Anekwe

GPs do not need to regularly monitor the blood pressure of their hypertensive patients, and indeed doing so can even be misleading, a new study concludes.

The research, published online by the BMJ, challenges the validity of the nine-month monitoring interval recommended in the QOF.

It reports that regular checking is a poor method of detecting response to treatment and calls for an ‘urgent' review of current guidance.

The researchers warned regular readings had ‘a low probability of yielding reliable information about true changes in blood pressure'. They said GPs instead be leaving well over a year between readings to increase the chances of getting accurate information.

Their study examined the probability that blood pressure readings taken in patients at regular intervals after diagnosis actually reflected true changes in blood pressure, or false positives.

Readings were taken in 1,709 patients at the time of diagnosis, and then at three, six, nine and 15 months, and then every six months for a 33-month follow up period.

The researchers calculated the variance of blood pressure readings over the study period and estimated a patient with a baseline reading of 120mmHg would have a 1.2% chance of genuinely experiencing a sharp increase to 140mmHg.

But they found that in practice 6% of patients would record a reading at this level, with large numbers of false positives.

Study leader Dr Katherine Keenan, an Australian GP and researcher in public health at the University of Sydney, concluded there was little evidence to support the practice of regular blood pressure checks.

‘The probability that an apparent increase in blood pressure was a true increase rather than a false positive was still not much better than 50% if the first monitoring interval was left until nearly two years after the start of monitoring.

‘Longer intervals between measurements increase the probability that an observed increase in blood pressure is real, but the capacity of monitoring to distinguish true increases in blood pressure is poor even if monitoring is left several years.'

Dr Kathryn Griffith, a GP in York and president elect of the primary care cardiovascular society, said: ‘This study suggests checking blood pressure every three or six months is probably not necessary in patients whose blood pressure is stable.

‘But for patients at higher risk we should keep monitoring more regularly, or ask patients to take their blood pressure readings at home. Seeing patients regularly reinforces the message that hypertension is important and taking drugs is important.'

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