Accuracy of the pressure scale of sphygmomanometers in clinical use within primary care

Background It is widely recommended that sphygmomanometers are maintained and calibrated regularly to ensure that the pressure scale remains accurate to within the European Standard specification of +/- 3 mmHg. In primary care, however, such checks are reported to be only rarely performed. This paper describes a survey of the accuracy of the absolute static pressure scale of aneroid, mercury and automated sphygmomanometers in clinical use in primary care. Methods On-site measurements of sphygmomanometer pressure scale accuracy were carried out in 45 general practices within Lambeth, Southwark and Lewisham. A total of 279 sphygmomanometers from these practices were included in the study. The device pressure scales were calibrated using an accurate electronic reference pressure sensor. Results The key finding of this study is that 179% (50 out of 279) of all surveyed devices gave errors exceeding the 3 mmHg threshold. Of these, 53.2% (33 out of 62) of aneroid devices were found to be reading in error by more than 3 mmHg compared with 7.8% (116 out of 217) of the combined population of mercury and automated devices. The difference between these groups is statistically significant (P = 0.002). Significant differences in the performance of specific models of aneroid, mercury and automated devices were also identified. Conclusion A service model for improving the accuracy of blood pressure monitoring in primary care needs to take into account the current proliferation of pressure scale errors in these devices, the lack of uptake of regular checks and the poor quality of some of the devices currently in use.