BACKGROUND: Guidelines propose classification of conventional blood pressure (CBP) into normotension (<120/<80 mm Hg), prehypertension (120-139/80-89 mm Hg), and hypertension (≥140/≥90 mm Hg).

METHODS: To assess the potential differential contribution of ambulatory blood pressure (ABP) in predicting risk across CBP strata, we analyzed outcomes in 7,826 untreated people recruited from 11 populations.

RESULTS: During an 11.3-year period, 809 participants died (276 cardiovascular deaths) and 639, 383, and 225 experienced a cardiovascular, cardiac, or cerebrovascular event. Compared with normotension (n = 2,639), prehypertension (n = 3,076) carried higher risk (P ≤ 0.015) of cardiovascular (+41%) and cerebrovascular (+92%) endpoints; compared with hypertension (n = 2,111) prehypertension entailed lower risk (P ≤ 0.005) of total mortality (-14%) and cardiovascular mortality (-29%) and of cardiovascular (-34%), cardiac (-33%), or cerebrovascular (-47%) events. Multivariable-adjusted hazard ratios (HRs) for stroke associated with 24-hour and daytime diastolic ABP (+5 mm Hg) were higher (P ≤ 0.045) in normotension than in prehypertension and hypertension (1.98 vs.1.19 vs.1.28 and 1.73 vs.1.09 vs. 1.24, respectively) with similar trends (0.03 ≤ P ≤ 0.11) for systolic ABP (+10 mm Hg). However, HRs for fatal endpoints and cardiac events associated with ABP did not differ significantly (P ≥ 0.13) across CBP categories. Of normotensive and prehypertensive participants, 7.5% and 29.3% had masked hypertension (daytime ABP ≥135/≥85 mm Hg). Compared with true normotension (P ≤ 0.01), HRs for stroke were 3.02 in normotension and 2.97 in prehypertension associated with masked hypertension with no difference between the latter two conditions (P = 0.93).

CONCLUSION: ABP refines risk stratification in normotension and prehypertension mainly by enabling the diagnosis of masked hypertension.