In Clinical Practice, Masked Hypertension is as Common as Isolated Clinic Hypertension: Predominance of Younger Men

Background The prevalence and implications of masked hypertension are under investigation. The aim of this study was to investigate the clinical characteristics associated with masked hypertension in subjects referred for ambulatory blood pressure (BP) monitoring. Methods We analyzed 1494 BP monitoring sessions. A subject was considered to have isolated clinic hypertension if clinic BP was ≥140/90 mm Hg and awake BP was <135/85 mm Hg. Masked hypertension was diagnosed when clinic BP was <140/90 mm Hg and awake BP was ≥135/85 mm Hg. Results Of 1494 individuals, 16% had normal BP, 11% had isolated clinic hypertension, 61% had hypertension, and 11% had masked hypertension. Subjects with masked hypertension were younger and more likely to be male than subjects with isolated clinic hypertension, and their awake heart rate was significantly higher. A negative correlation was found between the awake-clinic systolic BP difference and clinic systolic BP (r = −0.7, P< .0001). The reproducibility of the masking phenomenon was comparable to that of other variables. Conclusions In a group of consecutive subjects referred for ambulatory BP monitoring, masked hypertension was found to be as common as isolated clinic hypertension. Masking was correlated with male sex, young age, and higher awake heart rate, thus suggesting a causal relationship with greater daytime physical activity. The linear association of the masking and the white-coat effects to clinic BP suggests that regression toward the mean may partially explain these phenomena.