Researchers from Birmingham and Oxford analysed data from 710 patients who attended a hypertension clinic at University Hospital Birmingham. At a pre-clinic appointment, they had blood pressure measured in one arm, and then the opposite arm immediately after. They were then fitted with a 24-hour ambulatory blood pressure monitor to the non-dominant arm, unless the difference in systolic pressure was over 20 mmHg or diastolic pressure over 10 mmHg, in which case the monitor was fitted to the arm with the higher reading.
There was a mean difference of 25.1 mmHg between the arm with the highest reading and the ABPM, compared with a mean difference of 15.5 mmHg between the arm with the lowest reading and the ABPM. When the inter-arm difference was calculated and compared to the ABPM, they found no significant association.
What does it mean for GPs?
The authors concluded that the study highlights ‘the limitations of single clinic readings, which are not accurate compared with ABPM or other forms of prolonged monitoring.’ They added that it reinforced NICE guideline advice that blood pressure should be measured in both arms and should be repeated if the difference in readings between the arms is more than 20 mmHg. They finished by saying that clinicians should ensure ‘the differences in right and left arm pressures are checked by repeated measures in both arms.’
Dr Terry McCormack, GP in Whitby and member of the NICE guideline development group for hypertension: ‘The study points out that unless you are using equipment which simultaneously takes BP in both arms you need to do a series of tests to be accurate. This is the perfect way to take blood pressure, but it remains to be seen if it is taken up in practice.’