March 29, 2016Open Access

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

Q: What is the clinical evidence from this study?

Study design: Cross-Sectional. Population: Blood pressure monitoring (n=61). Intervention: Time in service (>18 months) vs. Time in service (<18 months). Primary outcome: Monitor failure (difference from reference monitor of +/- 3 mmHg at any testing interval) (p=0.038).

JHJames HodgkinsonUniversity College Birmingham CKConstantinos KoshiarisPreventive Cardiology UMUna MartinApollo Hospitals

Key Result

Among 61 blood pressure monitors used in community pharmacies, 13% failed accuracy standards overall, with failure rates significantly higher for devices in service for over 18 months (29% vs 5%, P=0.038).

Study Design

Type

Cross-Sectional (n=61)

Multicenter

Yes

PICO

Population

61 validated automatic blood pressure monitors used for free blood pressure checks across 52 community pharmacies in central England.

Exposure / Comparator

Time in service (>18 months) vs Time in service (<18 months)

Primary Outcome

Monitor failure (difference from reference monitor of +/- 3 mmHg at any testing interval), p=0.038

Main Result

Absolute Event Rate: 29% vs 5%

p-value: p=0.038

Limitations

Weaknesses of the data surrounding length of usage and service duration, which were largely dependent on staff recall.
Small sample size of monitors with longer service duration due to the pharmacy chain's policy of replacing all monitors every 2 years.
Usage data from head office was only available at the pharmacy level, limiting its utility for individual monitors in pharmacies with multiple devices.

Abstract

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, 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.

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