Comparison of unattended, attended and routine clinic systolic blood pressure measurements and determinants of blood pressure difference between attended and unattended BP

The study compared unattended(uAOBP), attended(aAOBP) and routine clinic systolic blood pressures (SBP) and investigated the role of BP measurement sequence and aAOBP threshold on SBP difference between aAOBP and uAOBP. Eligible patients were randomized to the order of aAOBP and uAOBP measurements during a single clinic visit. aAOBP and uAOBP measurements were obtained under standardised conditions using an Omron HEM907 BP-monitor. Routine clinic BP(CBP) from the same visit was also obtained. 85 patients (mean age 69.9 ± 16.4 years, 52.9% males) underwent aAOBP and uAOBP measurements. CBP was available in 78. uAOBP was significantly lower than both aAOBP (mean difference 4.12 ± SD7.91 mmHg, P < 0.001) and CBP (mean difference 6.67 ± SD6.67 mmHg, P < 0.001). When comparing randomised groups, mean BP difference was significant in only those who underwent aAOBP measurement first (6.30 + 7.29 mmHg; P < 0.001), but not in those who underwent uAOBP measurement first (1.88 + 7.98 mmHg; P = 0.134). In subgroup analysis by aAOBP ≥130 mmHg(vs.<130 mmHg), the mean BP difference was significant in only those with an aAOBPs ≥130 mmHg (6.13 ± 0.07 mmHg, P < 001), but not in those with an aAOBPs <130 mmHg (1.63 + 7.05 mmHg, P = 0.162). Correlation and Bland-Altman analyses revealed closer correlation between uAOBP and aAOBP(r = 0.925, P < 0.001), with lower bias (4.12 mmHg) and narrower 95% limits of agreement (LoA) (-11.38, 19.62 mmHg), compared to clinic SBP (r = 0.784, P < 0.001; Bias: 6.67 mmHg; LoA:-20.67, 34.01 mmHg. An aAOBP of 140 mmHg corresponded to an uAOBP of 135.3 mmHg. Both CBP and aAOBP significantly overestimate uAOBP. BP differences are partly attributable to the sequence of BP measurement and the level of aAOBP.