Accuracy of monitors used for blood pressure checks in English retail pharmacies:
James Hodgkinson, Constantinos Koshiaris, Una Martin, Jonathan Mant, Carl Heneghan, FD Richard Hobbs and Richard J McManus
INTRODUCTION High blood pressure (BP) is a key risk factor for the development of cardiovascular disease1 and a major cause of morbidity and mortality worldwide.2 An accurate BP monitoring device is fundamental to BP measurement in the diagnosis and control of hypertension. Several protocols3–5 exist for the validation of BP measuring devices but these are generally undertaken and then published on brand new models, and so do not guarantee sustained accuracy thereafter. The revised General Medical Services contract for UK GPs (2003)6 includes a recommendation to ensure medical equipment is regularly maintained, calibrated and replaced if necessary. Typically, new monitors are assumed to be accurate for 2 years and then annual checks are undertaken. However, it is not clear whether this is appropriate, as the drift in accuracy over time of an automated sphygmomanometer is not known. The error rate is a function of random (variability) and systematic (bias) error, and ultimately depends on the calibration interval of the device, and the conditions under which it is used. Detection and control of hypertension are sub-optimal,7 and a recent study has identified that there are insufficient GPs in England to achieve high levels of detection while at the same time maintaining access to appointments with GPs.8 Community pharmacies are a good potential site for identifying cardiovascular risk factors and improving disease detection,9 including identifying people with hypertension, because of their accessibility and because many pharmacies provide free access to BP monitors. Pharmacists have been involved in successful community-based screening programmes developed to improve detection and treatment of hypertension, both in the UK and worldwide.10–16 Community pharmacy BP monitoring is readily available, widely demanded, and recommended by hypertension guidelines.11,17,18 Evidence from the US19 suggests that many people with hypertension check their BP at a pharmacy. In the UK, the ‘Know Your Numbers’ campaign has ensured that 1.5 million people have had their BP checked in the UK since 2001, mostly at community pharmacies.20 However, the few studies evaluating publicly available monitors have shown them to be inaccurate.21–27 Many of these studies are more than a decade old, and there remains limited evidence of how well the monitors maintain their rigour in a potentially challenging environment. Therefore, the authors assessed the accuracy of validated28 automatic BP monitors in a UK retail pharmacy chain, in which the current policy is to retire monitors after 2 years in service for free BP checks without interim calibration checks.