Background: Current guidelines make no recommendations on the optimal timing or number of measurements for assessing home blood pressure variability (HBPV). Our aim was to elucidate the optimal schedule for measuring HBPV in relation to cardiovascular risk.
Methods: In total, 1,706 Finnish adults (56.5 ± 8.5 years; 54% women) self-measured their home blood pressure (HBP) twice in the morning and evening during 7 consecutive days. The participants were followed up for cardiovascular events. We examined the association between HBPV (coefficient of variation based on 2 through 7 measurement days) and cardiovascular events using Cox regression models adjusted for HBP and other cardiovascular risk factors.
Results: During a follow-up of 11.8 ± 3.1 years, 216 cardiovascular events occurred. Systolic morning HBPV based on three (hazard ratio [HR], 1.039; 95% confidence interval, 1.006-1.074, model c statistic 0.737) through seven (HR, 1.057; 95% confidence interval, 1.012-1.104, model c statistic 0.737) measurement days was significantly associated with cardiovascular events. Agreement in classification to normal vs. increased morning day-to-day HBPV between consecutive measurement days became substantial (κ = 0.69 for systolic and κ = 0.68 for diastolic) after the fourth measurement day. The associations of diastolic HBPV, evening HBPV, all-day HBPV, and variability based on first measurements of each measurement occasion, with cardiovascular outcomes were nonsignificant or remained significant only after the sixth measurement day.
Conclusions: Our results suggest systolic HBP should be measured twice in the morning for at least 3 days when assessing HBPV. Increasing the number of measurement days from 3 to 7 results in marginal improvement in prognostic accuracy.