Masked Hypertension Definition
Masked hypertension is defined as normal blood pressure readings in the office/clinic setting (office BP <140/90 mmHg) but elevated blood pressure readings when measured outside the office setting using either ambulatory blood pressure monitoring (ABPM) or home blood pressure monitoring (HBPM). 1
Specific Diagnostic Criteria
According to the 2017 ACC/AHA guidelines, masked hypertension is diagnosed when:
- Office/clinic BP: Normal (<140/90 mmHg)
- Out-of-office BP (ABPM or HBPM): Consistently elevated above normal thresholds 1
The specific out-of-office thresholds that define hypertension are:
- Daytime ABPM: ≥135/85 mmHg
- Nighttime ABPM: ≥120/70 mmHg 2
- Home BP: ≥135/85 mmHg (generally accepted threshold)
Clinical Significance and Risk Profile
The cardiovascular disease and all-cause mortality risk in persons with masked hypertension is similar to sustained hypertension and approximately twice as high as normotensive individuals. 1 This makes masked hypertension a clinically critical diagnosis that should not be dismissed simply because office readings appear normal.
The relative risk for fatal and non-fatal cardiac/cerebrovascular events is 2.09 (95% CI: 1.80-2.44), which is comparable to sustained hypertension at 2.26 (95% CI: 1.84-2.78) 3.
Prevalence
The prevalence varies by population:
- General population surveys: 10-26% (mean 13%) 1
- Normotensive clinic populations: 14-30% 1
- When expressed as proportion of patients with normal office BP: 32% overall 3
- In treated patients (masked uncontrolled hypertension): Approximately 30% of those with controlled office BP 4
Masked Uncontrolled Hypertension
In patients already being treated for hypertension, the analogous condition is called "masked uncontrolled hypertension" - characterized by controlled office BP readings but uncontrolled BP in out-of-office settings 1. This has a prevalence of approximately 43% among treated patients with normal office readings 3.
Screening Recommendations
The 2017 ACC/AHA guidelines recommend (Class IIa, Level B-NR) screening for masked hypertension with HBPM or ABPM in adults with untreated office BPs consistently between 120-129 mmHg systolic or 75-79 mmHg diastolic. 1
Additional screening should be considered (Class IIb, Level C-EO) in treated patients with office readings at goal but who have target organ damage or increased overall cardiovascular disease risk 1.
Key Clinical Pitfall
The most common pitfall is assuming that normal office BP readings exclude hypertension entirely. Masked hypertension increases susceptibility to end-organ damage with a two-fold greater risk for cardiovascular events and kidney dysfunction 4, yet it remains frequently underdiagnosed because clinicians rely solely on office measurements.