Practice audits: reliability of sphygmomanometers and blood pressure recording bias

Abstract

It is well established that numerous errors, biases and omissions in recording blood pressure exist. This study had two objectives. Firstly, to measure the accuracy of sphygmomanometers used in general practice and secondly to assess digit bias in blood pressure recording. This study was carried out in the then Northfield PCG, which comprised 18 practices and 67 GPs. A total of 131 mercury and aneroid sphygmomanometers were tested for accuracy by a trained technician in accordance with the methods specified in BS 2743 (1990). Accuracy was defined as an error of greater than 10 mm Hg. The second part of the methodology involved undertaking an audit of the proportion of registered patients aged 35–80 years who had their blood pressure measured within the last 5 years by members of the Primary Health Care Team. The results were that of the mercury and aneroid sphygmomanometers tested, 17% were inaccurate. Of these, 4% recorded an error greater than 10 mm Hg. One percent of mercury and 10% of aneroid sphygmomanometers recorded an error greater than 10 mm Hg respectively. Sixteen (12%) sphygmomanometers were so deteriorated (air leaks, dirt in mercury) that the researcher suggested their immediate withdrawal from service. The results of the blood pressure recording audit suggested digit bias of both systolic and diastolic recordings to the nearest 10 mm Hg. This study suggests that sphygmomanometers used in general practice are very likely to be inaccurate and some may well be so deteriorated that they should be withdrawn from service. The results of the blood pressure audit showed digit bias in systolic and diastolic readings to the nearest 10 mm Hg. The implications for clinical care—both over diagnosis and under diagnosis—although not assessed are likely to be appreciable. PCG Clinical Governance teams in conjunction with Practice Clinical Leads must address these basic issues.