Accuracy of drug store blood pressure monitors: an observational study

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.

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.

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.

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.