What is masked hypertension and how is it diagnosed and managed?

Masked Hypertension: Comprehensive Clinical Overview

Definition and Clinical Significance

Masked hypertension is a dangerous condition where office blood pressure appears normal (<130/80 mm Hg) but out-of-office measurements reveal consistently elevated readings (home BP ≥135/85 mm Hg or daytime ambulatory BP ≥135/85 mm Hg), carrying cardiovascular risk equivalent to sustained hypertension and approximately double that of true normotension. 1, 2

Blood Pressure Thresholds for Diagnosis

Measurement Setting	Hypertensive Threshold
Office BP	Normal (<130/80 mm Hg)
Home BP	≥135/85 mm Hg
Daytime ABPM	≥135/85 mm Hg
Nighttime ABPM	≥120/70 mm Hg
24-hour ABPM	≥130/80 mm Hg

1, 2

Epidemiology and Prevalence

• Prevalence ranges from 10-26% (mean 13%) in population-based surveys and 14-30% in normotensive clinic populations 1
• In chronic kidney disease populations, prevalence reaches 28-43%, making this a particularly high-risk group requiring screening 3
• Approximately 30-40% of patients with masked hypertension progress to sustained hypertension within 5-10 years 2

Risk Factors and Associated Conditions

The following factors significantly increase the likelihood of masked hypertension and should trigger screening: 1, 2

• Younger age and male gender 1
• Active smoking and alcohol consumption 1, 2
• Physical activity and exercise-induced hypertension 1, 2, 4
• Obesity and diabetes mellitus 1, 2
• Chronic kidney disease 1, 2
• Family history of hypertension 1
• Office BP in the high-normal range (120-129/75-79 mm Hg) 1, 2

Cardiovascular Risk Profile

The cardiovascular disease and all-cause mortality risk in masked hypertension equals that of sustained hypertension and is approximately twice as high as true normotension. 1, 3

Target Organ Damage

Masked hypertension is associated with increased prevalence of: 1, 3, 5, 6

• Left ventricular hypertrophy 1, 5, 6
• Increased carotid intima-media thickness 1, 5, 6
• Microalbuminuria and impaired renal function 1, 3, 6
• Impaired large artery distensibility 5
• Increased risk of nephropathy, especially in diabetic patients when nocturnal BP is elevated 1

Diagnostic Approach

When to Screen

Screen for masked hypertension in the following clinical scenarios: 1

1. Untreated patients with office BP consistently 120-129/75-79 mm Hg (Class IIa recommendation) 1
2. Treated patients with office BP at goal but evidence of target organ damage or increased cardiovascular risk (Class IIb recommendation) 1, 2
3. Patients with multiple cardiovascular risk factors despite normal office readings 3, 2

Diagnostic Methods

Home blood pressure monitoring (HBPM) is the reasonable first-line screening tool, but ambulatory blood pressure monitoring (ABPM) is preferred for definitive diagnosis as it provides superior cardiovascular risk prediction. 1, 3, 2

HBPM Protocol

• Measure BP for 4-7 days 7
• Take readings twice daily (morning and evening) 7
• Diagnostic threshold: ≥135/85 mm Hg 1, 2

ABPM Protocol (Preferred)

• 24-hour monitoring provides daytime, nighttime, and overall BP patterns 1
• Daytime threshold: ≥135/85 mm Hg 1, 2
• Nighttime threshold: ≥120/70 mm Hg 1, 2
• 24-hour threshold: ≥130/80 mm Hg 1, 2

Important caveat: The overlap between HBPM and ABPM in diagnosing masked hypertension is only 60-70%, with disagreement occurring in 23-30% of cases. 1, 7 When HBPM suggests masked hypertension in high-risk patients, confirm with ABPM before initiating treatment 1, 3

Subtypes of Masked Hypertension

Recognizing the subtype guides targeted management: 6

• Morning hypertension (most common): caused by circadian variation, evening alcohol use, or short-acting antihypertensive drugs 6
• Daytime hypertension: associated with smoking, mental stress, or physical stress 6
• Nighttime hypertension: linked to high salt intake, renal dysfunction, obesity, sleep apnea, or autonomic failure 6
• Exercise-induced masked hypertension: exaggerated BP response to exercise predicts masked hypertension with 41% prevalence 4

Management and Treatment

Pharmacologic Therapy

Treat masked hypertension with antihypertensive medications using the same agents and targets as sustained hypertension, as cardiovascular risk is equivalent. 3, 2

First-Line Agents 3, 2

• Thiazide diuretics
• ACE inhibitors
• Angiotensin receptor blockers (ARBs)
• Calcium channel blockers
• Beta-blockers

For patients with markedly elevated out-of-office BP or high cardiovascular risk, consider initiating two-drug combination therapy, preferably as fixed-dose combinations to improve adherence. 3

Treatment Goals

Target out-of-office BP normalization to <130/80 mm Hg (home/daytime ABPM <135/85 mm Hg). 2

Lifestyle Modifications

Implement comprehensive lifestyle changes alongside pharmacotherapy: 3

• Weight reduction if overweight or obese 3
• Dietary modifications: reduced sodium intake and DASH diet 3
• Smoking cessation 3
• Limited alcohol intake 3

Masked Uncontrolled Hypertension

In treated patients, "masked uncontrolled hypertension" refers to controlled office BP but uncontrolled out-of-office readings, carrying similar cardiovascular risk as untreated masked hypertension. 1

Screen for masked uncontrolled hypertension with HBPM in treated patients with office BP at goal who have target organ damage or increased cardiovascular risk (Class IIb recommendation). 1

If HBPM suggests masked uncontrolled hypertension, confirm with ABPM before intensifying treatment (Class IIb recommendation). 1

Critical Clinical Pitfalls to Avoid

1. Never rely solely on office BP measurements for diagnosis or treatment monitoring in patients with suspected masked hypertension 3, 2 - this leads to underdiagnosis and undertreatment of a high-risk condition

2. Do not withhold treatment based on normal office readings when out-of-office measurements confirm hypertension 3, 2 - cardiovascular risk equals sustained hypertension regardless of office readings

3. Do not assume HBPM alone is sufficient for high-risk patients 1, 3 - ABPM provides superior cardiovascular risk stratification and should be used for confirmation when feasible

4. Do not assume normal office BP equals low cardiovascular risk without out-of-office confirmation in patients with risk factors 2

5. Avoid using long intervals between follow-up measurements 1 - periodic monitoring is essential as 1-5% per year convert to sustained hypertension, with higher rates in those with elevated BP, older age, obesity, or Black race

Monitoring and Follow-Up

After diagnosis, periodic monitoring with ABPM or HBPM is reasonable to detect transition to sustained hypertension (Class IIa recommendation). 1

The incidence of conversion from masked hypertension to sustained hypertension is 1-5% per year, with higher rates in patients with elevated BP, older age, obesity, or Black race. 1