Prevalence of masked hypertension in attended versus unattended office blood pressure measurement

There is a controversial debate regarding whether unattended blood pressure (BP) measurement should be regarded as the new gold standard of office BP measurement. Unattended BP measurement eliminates the white-coat effect and reduces external influences on the patient. On the other hand, it might underestimate real-life BP. The present study compares the prevalence of masked hypertension using attended versus unattended office BP measurements. We performed a cross-sectional study on 213 patients in a general practitioner's outpatient clinic and compared attended and unattended office BP with 24h-ambulatory BP monitoring (24h-ABPM). Masked hypertension was defined as pressure ≥135/85 mmHg in daytime ABPM with office systolic BP < 140/90 mmHg. Median attended and unattended office BPs were 140/86 and 134/80 mmHg with a median 24h-BP of 129/79 mmHg and daytime ABP of 133/82 mmHg. The number of patients with masked hypertension was 45/213 (21.2%) using unattended and 23/213 (10.8%) using attended office BP measurements (p < .0001). Bland-Altman analysis revealed a 7.4 mmHg systolic and 6.2 mmHg diastolic bias between the attended versus unattended office BP, and two systolic and -1.7 mmHg diastolic biases between the unattended office BP and daytime ambulatory BP. In linear regression analysis, an unattended office BP of 134 mmHg corresponded to 140 mmHg in attended BP measurement. Using a cut-off of 135/85 mmHg instead of 140/90 mmHg in unattended office BP measurement, the rate of masked hypertension was 26/213 (12.2%). Thus, unattended office BP measurement results in a substantial increase in the prevalence of masked hypertension using the traditional definition of hypertension. The present findings suggest that it might be reasonable to use a definition of 135/85 mmHg.