Classification of blood pressure levels by ambulatory blood pressure in hypertension

Whereas clinic blood pressure (CBP) above normality is divided into stages, no corresponding classifications are available for 24-hour ambulatory blood pressure (ABP). We conducted a study (1) to define stages of hypertension by ABP corresponding to CBP stages and (2) to evaluate if these stages have prognostic impact similar to CBP stages. Seven hundred thirty-six hypertensive patients were included. Mean systolic blood pressure was 149+/-15.2/87+/-8.6 mmHg for CBP and 135+/-13/79+/-9.7 mmHg for ABP. The mean bias between both methods was -13.3 mm Hg (95% CI, -14.3 to -12.2; 1.96xSD limits of agreement, 15.7 to -42.3) and -7.3 mm Hg (95% Cl, -7.9 to -6.6; 1.96xSD limits of agreement, 9.8 to -24.3) for systolic and diastolic blood pressure (P>0.0001 for both), respectively. Classification of hypertension by ABP revealed lower cutoff values for the different stages of hypertension compared with the corresponding cutoff values for CBP (CBP versus ABP: 140/90 versus 132/81 mm Hg; 160/100 versus 140/88 mm Hg; 180/110 versus 148/94 mm Hg, P<0.001). Overall, 82 (11.1%) patients had nonfatal clinical cardiovascular events and 9 (1.2%) patients died of a cardiovascular cause during follow-up. The distribution of cardiovascular events was significantly associated with increasing ABP value (P<0.006). Staging of hypertension by ABP may facilitate the use of this method in daily clinical practice, as ABP can now be used not only to confirm the diagnosis of hypertension but also to assess the severity and prognosis of hypertensive disease.