Criteria for Diagnosing Hypertension
Hypertension is diagnosed when blood pressure measured in 2-3 office visits is ≥140/90 mmHg, or when out-of-office measurements confirm elevated blood pressure according to specific thresholds. 1, 2
Blood Pressure Measurement Protocol
Office Blood Pressure Measurement
Environment and preparation:
- Quiet room with comfortable temperature
- Patient should avoid smoking, caffeine, and exercise for 30 minutes before measurement
- Empty bladder before measurement
- Patient should be seated and relaxed for 3-5 minutes before measurement
- No talking during measurements 1
Proper technique:
- Patient seated with back supported, feet flat on floor, legs uncrossed
- Arm resting on table with mid-arm at heart level
- Use validated electronic (oscillometric) upper-arm device
- Use appropriate cuff size (too small overestimates BP, too large underestimates) 1, 2
- Take 2-3 measurements with 1-minute intervals between readings
- Calculate the average of the last two measurements 2
Diagnostic Thresholds
According to the 2020 International Society of Hypertension guidelines:
| Classification | Systolic (mmHg) | Diastolic (mmHg) |
|---|---|---|
| Normal BP | <140 | <90 |
| Hypertension | ≥140 | and/or ≥90 |
According to the 2017 ACC/AHA guidelines:
| Classification | Systolic (mmHg) | Diastolic (mmHg) |
|---|---|---|
| Normal | <120 | and <80 |
| Elevated | 120-129 | and <80 |
| Stage 1 Hypertension | 130-139 | or 80-89 |
| Stage 2 Hypertension | ≥140 | or ≥90 |
Diagnostic Process
Initial assessment:
- Obtain BP measurements on at least 2-3 separate occasions over a period of time 1
- For slightly elevated BP: measurements over several months
- For markedly elevated BP: measurements over weeks or days
- For severe elevation (≥180/110 mmHg): diagnosis can be made in a single visit, especially with evidence of cardiovascular disease 1
Confirmation with out-of-office measurements:
- Ambulatory Blood Pressure Monitoring (ABPM) or Home Blood Pressure Monitoring (HBPM) recommended to confirm diagnosis 1, 2
- Diagnostic threshold for 24-hour average BP: ≥130/80 mmHg
- Diagnostic threshold for home BP: ≥135/85 mmHg (average of readings) 2
- Helps identify white coat hypertension (high office BP, normal out-of-office BP) and masked hypertension (normal office BP, high out-of-office BP) 1, 2
Special considerations:
- White coat hypertension affects 10-30% of patients and requires lifestyle modification and follow-up
- Masked hypertension affects 10-15% of patients and may require pharmacological treatment 2
- Blood pressure variability should be considered, as it can vary significantly during the day and between days 2
Clinical Implications
- Multiple studies show that unconfirmed hypertension based on a single visit can lead to overestimation of prevalence by approximately 12.6% 3
- Proper diagnosis is crucial as hypertension is associated with increased risk of cardiovascular disease events and mortality 4
- Accurate diagnosis allows for appropriate treatment decisions, which can significantly reduce cardiovascular morbidity and mortality 4, 5
Pitfalls to Avoid
- Single-visit diagnosis: Except in cases of severe hypertension (≥180/110 mmHg), diagnosis should not be based on a single visit 1
- Improper measurement technique: Incorrect cuff size, patient positioning, or insufficient rest period can lead to inaccurate readings 1, 2
- Ignoring out-of-office measurements: Failure to confirm with ABPM or HBPM can miss white coat or masked hypertension 1, 2
- Neglecting blood pressure variability: BP naturally varies throughout the day and between days, which should be considered in diagnosis 1, 2
By following these evidence-based criteria for diagnosing hypertension, clinicians can ensure accurate identification of patients who require treatment, while avoiding unnecessary treatment in those with transiently elevated blood pressure.