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

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.