Objective: To determine ambulatory and home blood pressure means and d
istributions in relation to clinic blood pressure in a general populat
ion. Methods: We obtained a random sample of 2400 subjects stratified
by sex and 10 year age groups to be representative of residents aged 2
5-64 years of the city of Monza. Participation rate was 69% (1651 subj
ects). Blood pressure measurements consisted of clinic blood pressure
(average of three measurements, sphygmomanometry), home blood pressure
(average of morning and evening measurements, semiautomatic device) a
nd ambulatory blood pressure (automatic readings at 20 min intervals,
Spacelabs 90207). Clinic blood pressure was obtained both before and a
fter home and ambulatory blood pressures. Data analysis did not includ
e 213 subjects receiving antihypertensive drug treatment and was there
fore limited to 1438 participants. Results: In the 1438 subjects, clin
ic, home and ambulatory blood pressure showed a normal-like distributi
on, with a taller peak and a narrower base for ambulatory than for hom
e and clinic values. Clinic, home and ambulatory blood pressures were
significantly related to each other (P always <0.001). The means of th
e two clinic blood pressures obtained on consecutive days were superim
posable (127.4+/-17.0/82.3+/-9.8 and 128.2+/-16.5/81.9+/-9.9 mmHg) and
both were markedly higher than home and 24 h average blood pressures
(8.2 mmHg), which were similar to one another. The differences between
clinic and home or 24 h average blood pressure were similar in both s
exes but increased with increasing age and clinic blood pressure value
s. The influence of clinic blood pressure values on the clinic-ambulat
ory or clinic-home blood pressure differences was more important than
age. Although higher than the 24 h average value, daytime average bloo
d pressure was also lower than clinic blood pressure. Night-time blood
pressure was markedly lower than the daytime value in both sexes and
at all ages. Conclusion: Data from a large and unbiased sample of a ge
neral population show that home and 24 h or daytime average blood pres
sures are much lower than clinic blood pressure. The relatively close
correlation between blood pressure values measured with the different
methods used has allowed calculation of home and ambulatory blood pres
sure values corresponding to the accepted upper limit of normality of
clinic blood pressure (140/90 mmHg). The upper limit of normality for
the population was for both home and ambulatory blood pressures in the
range 120-130 and 75-81 mmHg for systolic and diastolic values, respe
ctively, with slight differences depending on sex and age. Taking 140/
90 mmHg as the upper normal limit of the population is therefore an er
ror that leads to individuals whose home or ambulatory blood pressures
are high being considered as normotensive.