What is the clinical evidence from this study?

Study design: Cross-Sectional. Population: Hypertension (n=584). Intervention: Digital sphygmomanometers vs. Aneroid sphygmomanometers. Primary outcome: Accuracy within 3 mmHg of the reference standard (p=0.001).

September 1, 2011Open Access

Type and accuracy of sphygmomanometers in primary care: a cross-sectional observational study

Key Result

Digital sphygmomanometers (88%) and mercury devices (95%) were significantly more likely to be accurate within 3 mmHg of a reference standard than aneroid models (78%).

Study Design

Type

Cross-Sectional (n=584)

Multicenter

Yes

Structured PICO

What is the type and accuracy of sphygmomanometers currently used in primary care?

Population

604 sphygmomanometers from 38 Oxfordshire primary care practices

Intervention

Evaluation of accuracy between 50 and 250 mmHg

Comparator

Reference standard (Omron PA350 or Scandmed 950831-2 pressure meters)

Outcome

Accuracy within 3 mmHg of the reference standardsurrogate

Digital sphygmomanometers have largely replaced mercury models in primary care and demonstrate equivalent accuracy, whereas aneroid devices have higher failure rates.

Main Result

Absolute Event Rate: 88% vs 78%

p-value: p=0.001

Limitations

Testing was undertaken in one geographical area that may not be representative of the country as a whole.
A minority of the practices had participated in an earlier pilot study and so were likely to perform better.
Practices that decided not to participate may be less interested in the topic and therefore less likely to maintain their equipment, potentially overestimating true device accuracy.
Not enough low-cost digital devices from high street pharmacies were tested to assess their performance separately.

Abstract

BACKGROUND: Previous studies identified worrying levels of sphygmomanometer inaccuracy and have not been repeated in the era of digital measurement of blood pressure. AIM: To establish the type and accuracy of sphygmomanometers in current use. DESIGN AND SETTING: Cross-sectional, observational study in 38 Oxfordshire primary care practices. METHOD: Sphygmomanometers were evaluated between 50 and 250 mmHg, using Omron PA350 or Scandmed 950831-2 pressure meters. RESULTS: Six hundred and four sphygmomanometers were identified: 323 digital (53%), 192 aneroid (32%), 79 mercury (13%), and 10 hybrid (2%) devices. Of these, 584 (97%) could be fully tested. Overall, 503/584 (86%) were within 3 mmHg of the reference, 77/584 (13%) had one or more error of 4-9 mmHg, and 4/584 (<1%) had one or more error of more than 10 mmHg. Mercury (71/75, 95%) and digital (272/308, 88%) devices were more likely to be within 3 mmHg of the reference standard than aneroid models (150/191, 78%) (Fisher's exact test P = 0.001). Donated aneroid devices from the pharmaceutical industry performed significantly worse: 10/23 (43%) within 3 mmHg of standard compared to 140/168 (83%) aneroid models from recognised manufacturers (Fisher's exact test P<0.001). No significant difference was found in performance between manufacturers within each device type, for either aneroid (Fisher's exact test P = 0.96) or digital (Fisher's exact test P = 0.7) devices. CONCLUSION: Digital sphygmomanometers have largely replaced mercury models in primary care and have equivalent accuracy. Aneroid devices have higher failure rates than other device types; this appears to be largely accounted for by models from indiscernible manufacturers. Given the availability of inexpensive and accurate digital models, GPs could consider replacing aneroid devices with digital equivalents, especially for home visiting.

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