Long-term reproducibility of ambulatory blood pressure is superior to office blood pressure in the very elderly.

Although it is known that reproducibility of ambulatory blood pressure (BP) is superior to office BP in middle-aged subjects, little is known in older age groups. Hence, we compared the long-term reproducibility of ambulatory and office BP readings in subjects over the age of 75 years. A cohort of 72 subjects 75-90 years of age (mean, 82 years at baseline) had repeat office and ambulatory BPs 2 years apart under similar conditions. On the same day, patients underwent office BP measurements by a semi-automated device and then by ambulatory BP monitoring. Awake and sleep periods were divided according to a diary kept by each patient. The agreement between studies was assessed using the standard deviation of the differences (SDD) and Bland-Altman plots. There were minimal mean changes in office, 24-h, and awake and sleep mean BP values between baseline and 2 years later. The SDDs between visits were lower for 24-h BP compared with the office BP (11.7/5.9 mm Hg versus 17.8/9.0 mm Hg, P<0.01). The SDD for 24-h BP was also lower than the SDDs for the awake and sleep BP (P<0.05). Nocturnal BPs defined by absolute values were more reproducible than categories of dippers and non-dippers. These data demonstrate that long-term reproducibility of 24-h BP is superior to office measurements for very elderly subjects. In a clinical trial involving this age group, far fewer subjects would be required if 24-h BP was the primary efficacy endpoint rather than the office BP.