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Am Fam Physician. 2000;61(12):3714-3717

Self-monitoring blood pressure programs have been initiated to improve blood pressure control and management, and clinical outcomes, and to reduce the risk of cardiovascular morbidity and mortality. While many patients take and record their blood pressure at home, it is unknown whether they accurately report these readings to their primary care physicians. In other studies of self-reported measurements used as a form of disease management (e.g., diabetes, asthma), significant inaccuracies in self-monitoring have been shown. Johnson and associates compared self-reported with electronically-stored home blood pressure and heart rate readings in patients with controlled and uncontrolled hypertension.

Twenty-nine ambulatory subjects were identified by hypertension-related codes (stage 1 to 3 hypertension) from the International Classification of Diseases, ninth revision. Digital automatic blood pressure monitors were used in this single-blind, randomized trial. The study participants were instructed to measure their blood pressure (systolic and diastolic) and heart rate with the monitor three times a day at specified time intervals, and to record the readings in a diary for one week, for a total of 21 measurements. Controlled blood pressure was defined as a measurement of less than 140/90 mm per Hg and uncontrolled blood pressure was defined as a measurement of 140/90 mm per Hg or greater. Controlled heart rate was defined as a measurement of 100 beats per minute or less and uncontrolled heart rate was defined as a measurement greater than 100 beats per minute. Erroneous reporting was any difference between the blood pressure or heart rate measurements documented in the diary (systolic blood pressure–reported, diastolic blood pressure–reported and heart rate–reported) and measurements electronically stored on the monitor (systolic blood pressure–electronic, diastolic blood pressure–electronic, and heart rate–electronic).

Ninety-six percent of the subjects were prescribed at least one antihypertensive medication. Only one subject adhered to the protocol as defined at each of three time intervals. Twenty-three of 29 subjects deviated from the protocol and repeated blood pressure and heart rate measurements more than once at each interval and self-selected which pressure to record in the diary. The number of blood pressure measurements per week ranged from 30 to 83. When systolic pressures were repeated during an interval, there was an equal distribution between reporting the highest, lowest and average pressure in the interval. When diastolic blood pressures were repeated, the reading between the highest and lowest during the interval was most frequently reported. Overall, there were no significant differences between systolic blood pressure–electronic and systolic blood pressure–reported or between diastolic blood pressure–electronic and diastolic blood pressure–reported. Of the heart rate–electronic readings, 67.9 percent were identical to the heart rate–reported.

These results demonstrated that 46.9 percent of the systolic blood pressure–electronic readings and 24.5 percent of the diastolic blood pressure–electronic readings reflected uncontrolled hypertension. While blood pressure was uncontrolled, 12 participants recorded their blood pressure as less than 140 mm per Hg on at least one occasion. Conversely, 3.6 percent of controlled systolic blood pressure–electronic readings were recorded by seven participants as being 140 mm per Hg or greater. Erroneous reporting was evident in 20.9 percent of uncontrolled diastolic blood pressure–electronic readings, while 3.8 percent of controlled diastolic blood pressure–electronic readings were recorded as 90 mm per Hg or greater. Of heart rate readings, 43.5 percent were erroneously reported as being less than 100 beats per minute.

Results indicate that the value of patient-directed treatment and monitoring programs depends on the reliability of the data collected. In this study, erroneous reporting occurred more frequently when blood pressure was greater than 140/90 mm Hg or when heart rate exceeded 100 beats per minute. In cases in which erroneous reporting was evident, subjects were more likely to falsely create and record blood pressures and heart rates that were not measured by the monitor rather than completely omit the measured result from the diary.

The authors conclude that although most self-reported blood pressure and heart rate readings were identical to the digitally stored measurements, erroneous reporting occurred significantly more often in cases of elevated blood pressure and heart rate, which could misguide physicians in making management decisions. If physicians perceive a disparity between home and office readings, they should initially validate the accuracy of the monitor by calibrating it against a standard mercury sphygmomanometer and consider “white-coat” hypertension and false reporting. If false reporting is suspected, a 24-hour ambulatory blood pressure monitor or a digital blood pressure monitor can be used.

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