How many times should blood pressure be measured at home for better prediction of stroke risk? Ten-year follow-up results from the Ohasama study

Objective To determine the optimum number of blood pressure self-measurements taken at home (home blood pressure) in relation to their predictive value for stroke risk. Methods We obtained more than 14 measurements of home blood pressure from 1491 people aged greater than or equal to 40 years without a history of stroke in the general population in Japan, and followed them up after a mean period of 10.6 years. The prognostic significance of blood pressure for stroke risk was examined using the Cox proportional hazards regression model, which was adjusted for possible confounding factors. Results The predictive value of home blood pressure increased progressively with the number of measurements, showing the highest predictive value with the average of whole measurements (mean = 25 measurements, 35% increase in the risk of stroke per 10 mmHg elevation in blood pressure). The initial home blood pressure values (one measurement) showed a significantly greater relation with stroke risk than conventional blood pressure values (mean of two measurements) (19/8% increase in the risk of stroke per 10 mmHg elevation in initial home/conventional systolic blood pressure values, respectively). Conclusions There was no threshold for the number of home blood pressure measurements within the range of 1-14 measurements for increasing the predictive power of stroke risk, suggesting that as many measurements as possible, preferably more than 14 measurements, is recommended for better prediction of stroke risk. It should be emphasized that home blood pressure has a stronger predictive power than does conventional blood pressure, even for a lower number of measurements. (C) 2004 Lippincott Williams Wilkins.