Accuracy of monitors used for blood pressure checks in English retail pharmacies: a cross-sectional observational study

Background Free blood pressure (BP) checks offered by community pharmacies provide a potentially useful opportunity to diagnose and/or manage hypertension, but the accuracy of the sphygmomanometers in use is currently unknown. Aim To assess the accuracy of validated automatic BP monitors used for BP checks in a UK retail pharmacy chain. Design and setting Cross-sectional, observational study in 52 pharmacies from one chain in a range of locations (inner city, suburban, and rural) in central England. Method Monitor accuracy was compared with a calibrated reference device (Omron PA-350), at 50 mmHg intervals across the range 0-300 mmHg (static pressure test), with a difference from the reference monitor of +/-3 mmHg at any interval considered a failure. The results were analysed by usage rates and length of time in service. Results Of 61 BP monitors tested, eight (13%) monitors failed (that is, were >3 mmHg from reference), all of which underestimated BP. Monitor failure rate from the reference monitor of +/-3 mmHg at any testing interval varied by length of time in use (2/38, 5% < 18 months; 4/14, 29% > 18 months, P = 0.038) and to some extent, but non-significantly, by usage rates (4/22, 18% in monitors used more than once daily; 2/33, 6% in those used less frequently, P = 0.204). Conclusion BP monitors within a pharmacy setting fail at similar rates to those in general practice. Annual calibration checks for blood pressure monitors are needed, even for new monitors, as these data indicate declining performance from 18 months onwards.