Defining normal ambulatory blood pressure.

Providing normal reference values and the means to interpret such values in practice is an urgent issue requiring consensus. Five basic approaches to defining normalcy for 24 h blood pressures (BP) are considered: 1) the relationship of ambulatory blood pressure (ABP) to morbidity and mortality, 2) the relationship of ABP to end-organ involvement, 3) ABP levels in normal populations, 4) the relationship of ABP to clinic BP, and 5) the relationship of 24 h indices to risk. Although there now is considerable evidence demonstrating that ambulatory measurement correlates more strongly with end-organ damage, the first two approaches are scientifically the best. It will be some time before levels of normalcy can be derived. There is a large volume of data on population samples permitting derivation of normalcy for clinical practice. Rounded upper limits of normal can be calculated as 140/90 mm Hg for 24 h ambulatory pressure, 150/90 mm Hg for daytime pressure, and 130/80 mm Hg for nighttime pressure. There are, however, considerable differences for age and gender which need to be taken into consideration.