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GP blood pressure readings often inaccurate

Inaccuracies in the way recording devices are used are leading GPs to systematically underestimate blood pressure by 2-3mm Hg, research suggests.

Terminal digit bias, when blood pressure measurements are rounded up or down to zero, is leading to ‘worrying' numbers of hypertensive patients being misclassified and inappropriately treated.

Previous research has addressed concerns that terminal digit bias may reduce a GP's ability to accurately assess the effect of anti-hypertensive treatment. Because the mean change in systolic BP with treatment is 8mm Hg, rounding to the nearest zero may increase the apparent effect of treatment.

A primary care study of blood pressure records taken from a database of UK general practice records between 1996/7 and 2005/6 found that terminal digit bias has led to a 2-3 mm Hg underestimation of average systolic blood pressure.

There was also ‘wide variation' in terminal digit bias between practices, the researchers found.

Writing in the March issue of the Journal of Human Hypertension, the researchers concluded that ‘Terminal digit bias has reduced markedly... but the mean level of recorded BPs ending in zero is still three times that expected.'

Dr Wayne Harrison, a public health fellow at the University of Birmingham and lead author of the report, called for monitoring of terminal digit bias to be incorporated into future quality standards.

Dr Harrison said: ‘There is evidence that terminal digit bias may lead to potential misclassification and inappropriate treatment of hypertensive patients. The increase in variation observed between these practices may therefore lead to an increased variation in the quality of care given to their patients.'

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