Self-measurement of blood pressure: accuracy, patient preparation for readings, technique and equipment.

OBJECTIVE: Self-measurement of blood pressure is commonly performed by those persons with hypertension and is advocated in many national hypertension guidelines. We examined accuracy of readings, patient knowledge, and preparation for readings, technique and equipment.
DESIGN: The study was a prospective observational design. Sixty-nine hypertensive patients were recruited from a tertiary referral center and by newspaper advertisement. All patients had previously self-measured their blood pressure. The patients initially measured their blood pressure under direct supervision in a clinic using their usual preparation, technique and their own equipment. Then after a five-min rest, blood pressures were measured twice both by research nurse and the patient in an alternating sequence. The nurse used a standardized blood pressure measurement technique.
RESULTS: Inadequate patient knowledge and performance of measurement technique and inaccurate equipment was common. The average initial patient systolic reading prior to the five-minute rest was higher than that of the trained nurse (9.1 +/- 13 mmHg systolic, p < 0.001 and 1.5 +/- 8.0 mmHg diastolic, p = 0.12). Almost half (42%) of the initial patient blood pressure readings differed in classification of hypertension/normotension from the nurse. The difference between the patient and nurse readings after the five-min rest was 3.8 +/- 11.8 / 1.1 +/- 6.8 mmHg.
CONCLUSIONS: Care must be taken in interpreting patient self-measured blood pressure unless there has been adequate training and assessment of patient and equipment accuracy. Studies of health care professionals reveal similar problems therefore widespread efforts to standardize blood pressure measurement are necessary.