P-29: The reliability of patient self-reported blood pressures

Like home glucose monitoring, self-monitoring of blood pressure has the potential to actively involve patients in disease management and control. Additionally, recent literature suggests that outpatient blood pressures, compared to office readings, may better predict the presence of left ventricular hypertrophy, and cardiovascular mortality risk. The objective of this prospective, single blind cohort study was to analyze the reliability of patient self-reported blood pressures over six months in an urban, university-based family practice. We recruited a convenience sample of 50 treated subjects with JNC Stage 1 or 2 hypertension. A trained research assistant instructed the subjects in home blood pressure monitor use. They were asked to check outpatient pressures twice weekly, for six months. Patients, unaware that the monitor electronically stores blood pressure readings, were asked to record their pressures in a written calendar diary designed especially for the study. Over the six-month study period, half the subjects recorded blood pressures that agreed with stored monitor values at least 80% of the time. Additionally, comparing means of matched readings (stored monitor reading with a corresponding self-reported diary value) and unmatched readings (monitor reading with no corresponding diary value), two-thirds of patients' mean readings were within 5 mm of each other for both systolic and diastolic pressures. As we did not instruct patients to limit their use of the monitor, 83% of patients had stored monitor readings that they did not record in their diaries, while 11% reported diary readings without corresponding monitor values. We conclude that a large proportion of our sample of primary care patients consistently reported their blood pressures accurately, sustained over six months. In certain patients, self-reported blood pressures are accurately reported over a sustained period of time, potentially providing useful information to physicians regarding daily variations in blood pressure.