'Home hypertension': exploring the inverse white coat response

The classical 'white coat response' to blood pressure measurement has been studied thoroughly. However, little is known about patients showing a reverse pattern, i.e. who have lower blood pressure readings at the clinic than outside healthcare facilities.

To estimate the proportion of patients whose blood pressure levels as determined by self-measurements at home are higher than those taken at the clinic and to explore possible associations with demographic, clinical, and psychological variables.

Patients consecutively attending (n = 214) an academic family medicine department in Toronto, Canada, were eligible. Subjects aged below 16 years and those on psychotropic or blood pressure-lowering agents were excluded. The clinic-home blood pressure difference (CHBPD) was calculated for each participating subject by subtracting home blood pressure from clinic blood pressure. Those who had negative values were compared with the rest of the sample.

A considerable proportion of patients had lower blood pressure at the clinic than at home (systolic, 34.6%; diastolic, 23.8%). These subjects did not differ from the rest of the sample with regard to age, sex, levels of education attained, immigration status, body mass index, experience of current symptoms, blood pressure levels, or psychological distress. However, in patients with a 'negative CHBPD', i.e. lower blood pressure at the clinic than at home, readings taken by an automatic, self-inflating device when still at the clinic were higher than in the rest of the sample.

The results point to measurement bias being at least partly responsible for higher blood pressure readings outside the clinic. Automatic measurement devices used for self/home blood pressure measurement seem to cause an alerting reaction analogous to the well-described 'white coat response'.