Blood pressure measurements taken at home are regarded as more representative of 24-hour blood pressures than measurements taken in medical clinics. The home measurements are believed to be essential to distinguish sustained elevations of blood pressure from “white coat” hypertension and may be better predictors of target organ damage and premature mortality than measurements taken by medical personnel. The increasing interest in home monitoring of blood pressure led Nordmann and colleagues to study the accuracy of measurements recorded by patients.
They asked 54 consecutive patients referred to a hypertension clinic for 24-hour ambulatory blood pressure monitoring to record blood pressure at home twice daily for 30 days. The patients were instructed in self-measurement techniques and were informed that the monitoring device had memory capacity. The patients were not told that their self-measurements would be compared to the stored automated measurements taken at the same time. Readings were considered correct if the timing (within 15 minutes) of measurements and the self-reported values (average of measurements ≤ 3 mm Hg) were identical to those recorded by the device.
All 54 patients completed the study. Overall, 72.8 percent of approximately 2,900 measurements were reported correctly. More than 80 percent of readings were reported correctly by 34 patients (63 percent). Twelve patients (22 percent) reported less than one half of all readings correctly. Patients showed no tendency to consistently report values too high or too low. When multiple regression analysis was used to identify factors associated with poor reporting accuracy, low education level was the only independent predictor. Patients with eight or fewer years of formal education were three times more likely than better-educated patients to report less than 80 percent of readings correctly.
The authors conclude that most patients reliably report accurate home blood pressure measurements but patients with low educational levels may be vulnerable to inaccurate recording of measurements.