Abstract
BACKGROUND: Ambulatory blood pressure (BP) (ABP) is a better predictor of adverse cardiovascular events than office BP (OBP). Owing to the extensive literature on the 'white coat effect', it is widely believed that ABP tends to be lower than OBP, with statements to this effect in Joint National Committee VII. However, recent evidence suggests that the difference varies systematically with age. METHODS: We searched PubMed to identify population studies, published before April 2009, which assessed OBP and either ABP or home BP (HBP). On account of significant heterogeneity in the outcomes, random effect models were used for the meta-analyses. RESULTS: OBP increased with age more steeply than awake ABP. OBP became higher than awake systolic/diastolic ABP at the age of 51.3/42.7 years in men (13 studies, N=3562) and 51.9/42.3 years in women (11 studies, N=2585). In the data in which OBP and HBP were measured (eight studies, N=4916), OBP was higher than HBP at all ages. In the data in which OBP, awake ABP, and HBP were all measured (two studies, N=895), awake ABP was higher than HBP at younger ages, becoming similar at the older age. CONCLUSION: OBP tends to be higher than awake ABP only after the age of 50 years for systolic and after the age of 45 years for diastolic BP, but is lower than ABP at younger ages; in contrast OBP tends to exceed HBP at all ages.