Masked hypertension (MH) is a relatively newly detected condition of which little is known. More information about MH may help to improve overall antihypertensive health care. We aimed to investigate the prevalence, potential causes, and associated consequences of MH. We searched published literature using MEDLINE, EMBASE, and the Cochrane database completed with references cited in reviews and original study articles. We restricted our research to articles written in the English, German, French, and Spanish language. Studies were included only when the prevalence of MH was reported, office blood pressure (BP) values were given, and methods of BP measurements were described in detail. All data were extracted independently by two readers with a standardized protocol and data-collection form. The prevalence of MH averaged 16.8% (95% confidence interval 13.0-20.5%). The MH prevalence was 7% for children and 19% for adults. MH prevalences did not differ significantly when determined with self or ambulatory BP measurement (21.1% vs. 16.8%; P = 0.42). Subjects with MH had significantly higher left ventricular mass index (LVMI) values than normotensives (110 vs. 98 g/m2; P < 0.01) but similar values as sustained hypertensives (109 g/m2). In addition, patients with MH were more often smokers than normotensives (mean difference 18%; P < 0.03). MH strikes about a quarter of the patients who were initially classified as normotensives (based on office BP measurements) and of treated hypertensives. Patients with MH seem to have a similar cardiovascular risk as sustained hypertensives but they may remain undetected. The presence of MH seems to be a matter of a coincidently low office BP value not related to certain subject characteristics although the chance of its presence may be increased by smoking and antihypertensive treatment.
