What is the accuracy of clinic blood pressure measurement?

In clinical practice, blood pressure (BP) is frequently measured at the end of the visit in patients sitting on one side of the bed and not on a chair according to guidelines.

In 540 consecutive subjects with essential hypertension (EH) attending a hospital outpatient clinic, BP was measured in the following sequence: 1) patient seated on chair for at least 5 min, 2) patient supine, 3) patient seated on bed, and 4) patient standing for a few minutes.

We found that mean (+/-SEM) BP was 143.5/87.2 +/- 0.9/0.5, 153.4/89.7 +/- 1.0/0.5, 148.9/90.9 +/- 1.0/0.5, and 144.8/91.7 +/- 1.0/0.6 mm Hg, respectively (P < .05 v position 1 for all). In 14% of patients, either systolic BP (SBP) or diastolic BP (DBP) was above the conventional upper limits of normality in the seated-on-bed but not in the recommended seated-on-chair position ("false" high clinic BP), whereas SBP and DBP were "false" normal (below limit for bed-seated and above limit for chair-seated position) in only 6% and 2% of patients, respectively. Overall, SBP and DBP increments from the chair- to the bed-seated position were inversely related to the baseline chair-seated values; systolic increments were directly related to age, in particular in the subgroup of untreated EH (n = 70), and to body mass index. A gender-related difference was apparent, as female subjects had more pronounced increments in SBP (+7.4 +/- 0.8 v +3.5 +/- 0.7 mm Hg) and DBP (+4.4 +/- 0.5 v 2.9 +/- 0.4 mm Hg) than did male subjects (P < .05 for both).

Clinic SBP and DBP are overestimated in the bed-seated position at the end of the visit compared with the recommended chair-seated position in treated and untreated patients with EH, in particular in elderly obese women with mild hypertension.