Aw-ad-2: association between ambulatory blood pressure and risk of home hypertension in a normotensive population

Objective: Most of the hypertension management guidelines recommend out-of-office blood pressure (BP) measurement such as self-measured BP at home (home BP) and ambulatory BP monitoring for the accurate diagnosis and management of hypertension. Both out-of-office BP measurements are more useful than office BP as prognostic indicators of cardiovascular risk. However, no prospective study has assessed the longitudinal association between the two types of out-of-office BP measurements. Therefore, we investigated the association between ambulatory BP and the risk of home BP-based hypertension in a normotensive population and whether considering ambulatory BP improves the 10-year prediction model for home hypertension risk, which was developed in the previous study. Desigh and method: We followed up 410 participants (83.2% women; age, 53.6 years) without home and ambulatory hypertension in the general population of Ohasama, Japan. The Cox model was used to assess the hazard ratios for home hypertension (home BP ≧135/≧85 mmHg or initiation of antihypertensive treatment). In addition, the predictive ability for home hypertension incidence between the models adjusted for the covariates with 24-h, daytime, or nighttime SBP was examined using Harrell's C-statistics, continuous net reclassification improvement (NRI), and integrated discrimination improvement (IDI). The NRI considers changes in the estimated prediction probabilities that imply a change from one category to another between different models. IDI is defined as the difference between the discrimination slopes of a basic model and an extended model. Results: During a mean 14.2-year follow-up, 225 home hypertension incidences occurred. The hazard ratio (95% confidence interval) for home hypertension incidence per 1-standard deviation increase in 24-h systolic BP (SBP) was 1.59 (1.33–1.90) after adjustments for possible confounding factors, including baseline home SBP. Harrell's C-statistic was 0.72 (0.69–0.75) for the basic 10-year risk prediction model, which includes sex, age, BMI, current or ex-smoker status, office SBP, and baseline home SBP. By adding 24-h, daytime, or nighttime SBP to the basic model, continuous NRI and IDI significantly improved although no significant improvement in Harrell's C-statistics was observed. Conclusions: Independent of the baseline home SBP, 24-h SBP was associated with the risk of home hypertension in a normotensive population. The prediction model for home hypertension risk was improved by the addition of 24-h SBP to the basic model. It could be useful to measure ambulatory BP for the early detection of home hypertension.