Accuracy of home blood pressure readings: monitors and operators

OBJECTIVE: To evaluate the accuracy of automated digital blood pressure monitoring devices and operators in the community. Also, we tested the effects of a simple education program, and looked for arm-arm differences. DESIGN: Subjects who had bought their own automated digital blood pressure monitor were recruited via an advertisement in the local newspaper. On arrival, they were asked to record their blood pressure exactly as they would at home. The investigator noted any technique deficiencies then corrected them. Blood pressures were then recorded by the investigator and the subject, on opposite arms, simultaneously, and repeated with the arms switched. Finally, subjects recorded their blood pressure again. The subjects' readings were compared to the average of monitor and mercury readings using Bland-Altman methods. RESULTS: A total of 80 subjects were tested. Before educating, subjects' systolic blood pressure (SBP) readings were +5.8+/-6.4 (standard deviation) mmHg greater than the mean of all readings, and diastolic blood pressure (DBP) were +1.3+/-4.0 mmHg; after educating they were +1.3+/-4.0 and -1.3+/-2.7 respectively. The monitors, as a group, were accurate, and met British Hypertension Society and AAMI highest standards. We found no differences among monitors that had been validated (n=26) and those that had not. There were differences between the arms: 5.3+/-5.2 mmHg for SBP and 3.4+/-3.3 mmHg for DBP. Most patients had never been informed by anyone of proper blood pressure measuring techniques. CONCLUSIONS: We conclude that home blood pressure measurement, as practiced in our community, is prone to error, mostly due to mistakes by the operator. These can easily be corrected, so that readings become more accurate. Attention should be paid to arm-arm differences.