Prevalence of Masked Hypertension in Subjects Treated with Antihypertensive Drugs as Assessed by Morning versus Evening Home Blood Pressure Measurements: The J-HOME Study

To investigate the relationship between morning and evening home blood pressure (BP) measurements to make a diagnosis of masked hypertension, we collected information on the characteristics of 3,303 essential hypertensive outpatients receiving antihypertensive medication in Japan using a physician, self-administered questionnaire. All patients were asked to measure their home BP once every morning and once every evening for two weeks. Morning and evening home BP values of each patient were defined as the average of all morning and all evening home BP values, respectively. The mean BP values of all study subjects were 142.8/80.6 mmHg for office BP, 139.8/81.8 mmHg for morning home BP, 133.7/76.9 mmHg for evening home BP, and 136.8/79.3 mmHg for the average of the morning and evening home BPs. Masked hypertension was defined as an office BP < 140/90 mmHg and a home BP > or = 135/85 mmHg. The prevalence of masked hypertension diagnosed using morning home BP (23.1%) was higher than that diagnosed by evening home BP (14.7%); the prevalence was 19.0% when diagnosed using the average of the morning and evening home BPs. Among the 1,386 patients with a normal office BP, the diagnosis of masked hypertension based on morning and evening home BP values differed in 28.8% of patients for systolic BP and 20.9% for diastolic BP (kappa coefficient = 0.43). The present study showed that the prevalence of masked hypertension was underestimated when the diagnosis of masked hypertension was made on the basis of evening home BP.