Accuracy of drug store blood pressure monitors: an observational study

Abstract

Objectives: Publically accessible blood pressure monitors are widely used, but little information is available on their accuracy. We compared blood pressure readings of 17 drug store monitors with those obtained using a validated home monitor (Omron BP742CAN) and both with those taken at home using the Canadian Hypertension Education Program protocol.

Materials and methods: Duplicate readings were taken using the drug store monitor (VitaStat, n=6, and PharmaSmart, n=11) on the left arm and the Omron on the right in three participants: two normal and one untreated hypertensive patient. We used Bland-Altman methods for comparison. We explored the correlation with average home blood pressure readings.

Results: Home average blood pressure for our three participants was 121±6/73±5, 106±6/62±4, and 142±8/81±7 mmHg. The mean systolic blood pressure difference (drug store-Omron) was -1.8±8.2 mmHg. Diastolic pressure difference was 1.7±5.6. Individual paired systolic differences varied from -19 to 14 mmHg. For the participant who required a large cuff, drug store systolic readings tended to be higher (4.1±6.7). In our three participants, drug store monitors as a group read higher than home systolic blood pressure: 7.5 [95% confidence interval (CI) 1.5-13.4], 1.2 (95% CI -4.0 to 6.4), and 1.0 (95% CI -2.5 to 4.4) mmHg. Diastolic blood pressure and heart rate differences were similar in magnitude.

Conclusion: On average, drug store monitors recorded lower systolic blood pressures and higher diastolic blood pressures than a validated monitor, but the difference was neither statistically nor clinically significant. Single reading comparisons showed a much broader range. In three participants, drug store monitors did reflect the average home blood pressure.