Ambulatory blood pressure monitoring: is the daytime period enough for making clinical decisions?

Aim: To assess the agreement between the clinical information provided by the ambulatory daytime average and 24 h average blood pressure value for diagnosing hypertension and assessing the effects of antihypertensive treatment.

Methods: We analysed 261 24 h ambulatory monitoring records (SpaceLabs 90207, SpaceLabs, Redmond, Washington, USA) obtained from hypertensives over 18 years of age (mean age 55.8 years) in order to make a diagnosis of hypertension or assess its control in response to treatment. Recording was programmed to occur every 20 min during waking periods and every 30 min during sleep, daily activity also being registered. The criteria compared in the diagnosis of hypertension were: (1) the evaluation criterion: an average blood pressure for the activity period of less than 135/85 mmHg (Joint National Committee VI); (2) the gold standard: an average blood pressure over 24 h of less than 125/80 mmHg (World Health Organization-International Society of Hypertension, 1999).

Results: In 90% of the records, there was agreement between both criteria. In 7.2%, the awake blood pressure average was normal and the 24 h average high. Values obtained were: sensitivity, 89% (95% confidence interval 84-89%); specificity, 92% (95% CI 88-95%); positive predictive value, 95.6% (95% CI 93-98%); negative predictive value, 81% (95% CI 75-85%); pretest probability, 66% (95% CI 60-72%); positive likelihood ratio, 11; and negative likelihood ratio, 0.3. There were no significant differences in age, gender or percentage of treated subjects between the groups with and without agreement.

Conclusions: Daytime and 24 h average blood pressure may indeed carry similar information for diagnosing hypertension and assessing the effects of antihypertensive treatment in clinical practice. Ambulatory blood pressure monitoring used only during the daytime period could be better tolerated and agreed to by patients than 24 h monitoring.