How is hypertension diagnosed?

How to Diagnose Hypertension

Hypertension is diagnosed when office blood pressure is ≥140/90 mm Hg confirmed across 2–3 separate visits spaced 1–4 weeks apart, with out-of-office confirmation strongly recommended whenever possible. 1

Diagnostic Blood Pressure Thresholds

• Office/clinic measurement: ≥140/90 mm Hg 1, 2
• Home blood pressure monitoring: ≥135/85 mm Hg 3, 2
• 24-hour ambulatory monitoring: ≥130/80 mm Hg (24-hour average), ≥135/85 mm Hg (daytime), ≥120/70 mm Hg (nighttime) 2

Office Blood Pressure Measurement Protocol

Pre-Measurement Preparation

• Patient must avoid smoking, caffeine, and exercise for 30 minutes before measurement 1, 3
• Empty bladder and sit quietly in a comfortable-temperature room for 3–5 minutes before the first reading 1, 4
• Neither patient nor staff should talk before, during, or between measurements 1, 3

Proper Positioning

• Patient seated with back supported on chair, legs uncrossed, feet flat on floor 1, 3
• Arm resting on table with mid-arm at heart level 1, 3

Device and Cuff Selection

• Use a validated electronic (oscillometric) upper-arm cuff device 1, 3
• Cuff bladder must cover 75–100% of arm circumference; incorrect sizing causes false readings (smaller cuff overestimates, larger underestimates) 1, 3

Measurement Technique

• Take 3 measurements with 1-minute intervals between each 1, 4
• Calculate the average of the last 2 measurements for clinical decision-making 1, 4
• If the first reading is <130/85 mm Hg, no further measurement is required at that visit 1, 3
• Initially measure BP in both arms; if consistent difference >10 mm Hg, use the arm with higher readings for future measurements 1, 3

Number of Visits Required for Diagnosis

Standard Approach

• Usually 2–3 office visits at 1–4 week intervals are required to confirm hypertension 1, 4

Grade-Specific Timing

• Grade 1 hypertension (140–159/90–99 mm Hg): Repeat measurements over several weeks to months 4, 3
• Grade 2 hypertension (160–179/100–109 mm Hg): Confirm within 1 month, preferably with out-of-office measurements 4, 3
• Severe elevation (≥180/110 mm Hg): Diagnosis may be made on a single visit if cardiovascular disease is present 1, 4

Most Conservative Approach

• For borderline cases (140–160/90–100 mm Hg), the Canadian guidelines recommend measurements on 4–5 separate occasions before diagnosis 4, 3

Out-of-Office Blood Pressure Confirmation

Out-of-office measurements are more reproducible than office readings and correlate better with target-organ damage and cardiovascular outcomes. 4, 3, 5

Home Blood Pressure Monitoring Protocol

• Measure twice daily: morning (before medication) and evening (before bedtime) 4, 6
• Take 2–3 readings per sitting, 1 minute apart 4, 6
• Monitor daily for ≥1 week, discarding the first day's readings 4, 6
• This provides ≥12 readings for clinical decision-making 4, 6

When Out-of-Office Confirmation Is Essential

• Borderline office readings (130–159/85–99 mm Hg) require home or ambulatory confirmation 2, 7
• Suspected white-coat hypertension (high office, normal home BP) 3, 2, 7
• Suspected masked hypertension (normal office, high home BP) 3, 2, 7

Ambulatory Blood Pressure Monitoring

• 24-hour ABPM is the gold standard for confirming hypertension 2, 7
• Particularly valuable for detecting nocturnal hypertension and assessing circadian BP patterns 7
• Critical for confirming true resistant hypertension and excluding pseudo-resistant hypertension 1, 7

White-Coat vs. Masked Hypertension

White-Coat Hypertension

• Office BP ≥140/90 mm Hg, home/ambulatory BP <135/85 mm Hg 2, 7
• Occurs in 10–30% of patients with elevated office readings 2
• Confers intermediate cardiovascular risk and does not require medication when overall risk is low and no organ damage is present 2, 7

Masked Hypertension

• Office BP <140/90 mm Hg, home/ambulatory BP ≥135/85 mm Hg 2, 7
• Found in 10–15% of patients 2
• Carries cardiovascular risk comparable to sustained hypertension and warrants pharmacologic treatment 2, 5

Initial Evaluation After Confirming Hypertension

Mandatory Laboratory Tests

• Serum sodium, potassium, creatinine, and estimated GFR 3
• Fasting blood glucose 3
• Lipid profile (at least total and HDL cholesterol) 3
• Urinalysis with dipstick for protein and blood 3
• 12-lead ECG 3

Physical Examination Focus

• Fundoscopic examination for retinopathy 1
• Pulse rate, rhythm, and character 3
• Carotid, abdominal, or femoral bruits (suggests renal artery stenosis) 1
• Diminished femoral pulses or arm-thigh BP discrepancy (suggests aortic coarctation) 1
• Signs of Cushing's syndrome (moon facies, central obesity, abdominal striae) 1
• Standing BP after 1 and 3 minutes in elderly or diabetic patients to detect orthostatic hypotension 1, 3

Critical Pitfalls to Avoid

• Never diagnose hypertension based on a single office visit (except BP ≥180/110 mm Hg with documented CVD) 1, 4
• Failing to allow 3–5 minute rest period before measurement leads to falsely elevated readings 1, 4, 3
• Talking during BP measurement artificially raises readings 1, 4, 3
• Using only the first reading markedly overestimates hypertension prevalence 4
• Incorrect cuff size causes systematic measurement errors 1, 3
• Not screening for white-coat or masked hypertension in borderline cases leads to misdiagnosis and mistreatment 3, 2, 7